BANNER Puget Sound view USGS home
Pacific Northwest geologic mapping and urban hazards

GDA (Geologic Data Assistant), an ArcPad Extension for Geologic Mapping: Code, Prerequisites, and Instructions

by Evan E. Thoms and Ralph A. Haugerud


U.S. Geological Survey
Open-File Report 2006-1097

Use of product or trade names in this report is for descriptive purposes only and does not constitute endorsement by the Geological Survey

Table of Contents

Download GDA
What you need to know
Required hardware and software

Windows CE / PocketPC PDA
GPS unit
Software on the laptop or desktop


Outline of GDA
GDA data structure
Base map and compilation geology

Setup instructions

Initial setup
To start a new project
Each time you start ArcPad

Data Safety
Incorporating GDA data into a desktop GIS
References Cited


GDA (Geologic Data Assistant) is an extension to ArcPad, a mobile mapping software program by Environmental Systems Research Institute (ESRI) designed to run on personal digital assistant (PDA) computers. GDA and ArcPad allow a PDA to replace the paper notebook and field map traditionally used for geologic mapping. GDA allows easy collection of field data that include:

  • Station location as determined by GPS, map inspection, or as a bearing and distance offset from an existing station

  • Map unit and related lithologies

  • Outcrop characteristics

  • Structural orientations

  • Contacts, faults, and other linear features

  • Information about samples

  • Information about photographs

  • Extended free-form text

  • Sketches

  • Miscellaneous map annotation

This report provides a link to downloadable code, describes the required hardware and software necessary to use GDA, describes the GDA data structure, gives setup instructions for GDA, describes moving data from GDA into a desktop GIS, and discusses customization of GDA. To use GDA efficiently will require an intermediate knowledge of computer systems and, most importantly, good file management. GDA does not have to be used in conjunction with ESRI's ArcMap, but knowledge of that program is useful for customizing certain GDA files and viewing shapefiles. Haugerud and Thoms (2004) discuss rationales behind some of the choices made in building GDA.

Note that the GDA code includes HTML help files that discuss setup and use of the software. Much of this report is copied from the GDA help files.

Download GDA

There are 2 downloadable GDA packages from which to choose depending on the intended host system.

  • For installation on a Windows PC, download This package contains the loose files and a simple DOS batch file to copy them to the appropriate directories. This is also the package to download for further development of GDA in ArcPad Application Builder.

  • For installation on a Windows CE device, download GDA_For_PPC.CAB.

Get a copy of this documentation as zipped html or PDF.

What you need to know

To use GDA, you should have some familiarity with your PDA, with ArcPad, and with some basic principles of GIS.

First, use your PDA. Learn how to open programs and switch between them. Experiment with the several different methods of text input, to find what works best for you. Learn how to change screen brightness. Poke around in the system settings. Windows CE has changed significantly with each release. Our experience is primarily with WinCE 3.0; if you are using a later version, some of our PDA-related advice may be wrong.

Configuring the communications link between the PDA and an external GPS receiver can be challenging. The instructions that work for our hardware and operating system are likely to be wrong for your setup. You will have read your manuals (this may not help much) and experiment.

Second, look through the ArcPad user manual (available here). Pay attention to the layer metaphor, the notion of an active layer, the limits of ArcPad symbolization, and how a map projection can be defined.

Third, you should have a basic understanding of map projections and datums. You should appreciate the distinction between the contents of a spatial database and the symbolization of those contents on a map or computer screen.

Required hardware and software

Windows CE / PocketPC PDA

ArcPad, and thus GDA, runs on the Windows CE 3.0 (or greater) operating system, also known as the PocketPC operating system. It can also be installed on Windows-based desktop, laptop, or tablet computers. It does not work on Palm or Linux devices. Most WinCE computers are adequate. When selecting a PDA, pay particular attention to display readability, communications capabilities, battery life, the quality of the digitizer, memory capacity, and speed. We are currently using Hewlett-Packard iPAQs with 400MHz processors, 64MB memory, and 240 x 320 pixel 16-bit color daylight-readable displays.

Extra battery

An extended-capacity battery, or an expansion pack with an additional battery, is desirable. You would like to have enough power for continuous operation throughout a 14-hour field day. When using a GPS it is especially useful to set your PDA to never shut off. One reason for this is simply efficiency, but the other is that turning a PDA off without first disconnecting the com port often causes the PDA to lock up so that it can only be reset with a soft reboot. The largest drains on the battery are the intensity of the backlight and the length of time it is on, so set your backlight to dim to nothing after a short period of inactivity.

Extra non-volatile memory

Use a Compact Flash card, Secure Digital card, or other non-volatile memory for mapping project workspace. This provides storage for large raster images and guards against data loss when, inevitably, you forget and let the PDA battery run down. We use expansion packs that provide both a Compact Flash slot and an additional battery. Be aware that unless you store programs in a non-volatile space on your PDA, ArcPad will evaporate from memory if the battery dies. As a backup in the field, keep a PC nearby from which you can re-install ArcPad.


Bluetooth (a short distance device-to-device radio protocol) is excellent for communication between the PDA and a GPS unit. Cable connections between GPS and PDA are fragile, inconvenient, and hard to make waterproof.

Screen protector

Protect the PDA screen from abrasion with a self-adhesive replaceable plastic screen protector (check Office Depot or a similar supplier.)


The PDA probably won't survive a 4-ft drop onto bedrock. Get a rugged case that provides significant shock-proofing. Consider third-party cases (such as Otterbox) as well as cases available through your PDA manufacturer. Such cases can also be waterproof, with a clear vinyl window over the PDA screen--but if you retain this window, omit any additional screen protector.

3rd-party stylus

A third-party stylus with a pocket clip or lanyard is handy. Multifunction instruments that combine a stylus with a pen or pencil (or both) are available for under fifteen dollars.

GPS unit

Standard recreational-grade GPS provides nominal XY accuracy of 10 meters (with averaging) at a cost of $100-300. We find this sufficient. For increased accuracy use a WAAS-capable GPS unit, or a differential GPS unit, at substantially greater cost. Note that ArcPad provides an excellent GPS display: all one needs is a screenless GPS receiver that that can send standard NMEA 0183 signals to another device.

GPS satellites broadcast at a wavelength that does not pass through the human body, so a pocket is not a good place from which to use a GPS unit. Instead, put it in the lid of a backpack, on the top of a staff protruding from a pack, or fastened it to your hat. Another option is to use a small external antenna on a hat (google on GPS Pathfinder Pocket Antenna Cap) while keeping the receiver in a pocket or on a belt clip (if you can tolerate the necessary connecting cables).

Communications between the GPS unit and PDA are a potential problem. If a cable connection is to be used you may have to purchase appropriate cables for both GPS unit and PDA separately, and you may have to join them with a male-to-male adapter and null modem connecter as well. See the ArcPad user manual for good instructions on following this route. Duct tape will transform the cables and adapter into a single, stronger, unit. The data-cable fitting on many PDAs is weak. One can mount the PDA in a rigid windowed box with a short data cable that leads from the PDA to a more substantial fitting anchored to the box and worry less about breaking the connector, but you will still be trussed up like Gulliver among the Lilliputians. A wireless connection (e.g. Bluetooth, see above) is better.

Compact flash card GPS units arguably provide the most robust connection. There are no cables, no risk of losing the signal due to distance from the receiver (as there is with Bluetooth devices), and since the GPS unit draws current from the PDA battery, there is no worry of having the unit die before your PDA does. They can also be swapped in and out of the compact flash slot with fewer com port hassles than the Bluetooth units. The main disadvantage with this method is that you are likely to lose the GPS signal as you hold the PDA near your body while entering data.

We use credit-card sized Bluetooth GPS receivers such as that sold by Socket Communications ( These 16-channel receivers can be bought for less than $230. They weigh 2 ounces and the replaceable and rechargeable battery lasts 9 hours, more than adequate for working out of a vehicle with a cigarette-lighter recharger available. For a long day on foot carry an extra battery or mobile recharger, such as the iPowerPak by Data Nation ( or Mobile Power Pack by Socket. 

In recent tests with a Bluetooth GPS unit and a Bluetooth-ready iPAQ h2200, we have found the Bluetooth Manager to be much improved over older versions, causing us to lean even more strongly toward that system.


ArcPad is a simple GIS program for the PocketPC, optimized for collection and display of map information while mobile. It has fewer symbolization and database capabilities than the average desktop GIS, can be customized to a limited extent using XML and VBScript, and has an excellent GPS interface.

ArcPad can be obtained from ESRI ( for about $500. A free evaluation copy that times out after 20 minutes may be downloaded from the web. GDA will not work with versions of ArcPad earlier than 6.0.1 We are using ArcPad 6.0.3. We have not experimented with this version of GDA on ArcPad 7.

Third party file browser

The file browsing program that comes with the Windows CE, File Explorer, does not, by default, show file extensions. Editing the registry to force file extensions to show is an option available to the advanced user, but it is risky. The safest remedy is to install a third party program that shows extensions. PEFile, by Vieka, is a cheap and reliable solution. Seeing file extensions is important because there are many files associated with GDA which have names that differ only by their extensions. Many can be edited in a text editor on the PDA by temporarily changing the extension to ‘.txt’.

Software on the laptop or desktop


ArcGIS or ArcView will make it easier to define symbolization, such as the colors of dots that correspond to different map units. See the ArcPad manual for advice on this. (Note that you can also do this with a text editor, carefully copying, pasting, and editing the .xml file for the layer. Colors are in RGB, 0..255 gamut for each component. Search for "VALUEMAPRENDERER".)

ArcGIS provides tools for reformatting data for digital base maps. You may need to reproject rasters to the projection of your field project. ArcGIS will export an entire map project to ArcPad. Note that you may have to tile large raster images to avoid the 50MB input-image size limit on the MrSID converter that is shipped with ArcGIS. See the ArcPad documentation.

You will almost certainly need ArcGIS or ArcView to make a completed geologic map from the data you collect with GDA.

Excel (or OpenOffice) or Access

You will need to edit .dbf files that constitute some of the picklists. This is conveniently done on a PC with Microsoft's Excel. The Calc program in works equally well. CDBF (google for it) works well. Another solution is to create an Access database containing all of the picklist tables and export them as needed in .dbf format. Let us know if you find a DBF editor that runs on a PDA!

Text editor

A text editor that works gracefully with plain ASCII files is handy for minor modifications of layer definition (.apl) and VBScript (.vbs) files. On a Windows platform, WordPad and Notepad are fine. Many other editors are available. Avoid using Microsoft Word because it may add hidden and extraneous formatting tags that are not recognized by GDA.


Outline of GDA

GDA consists of 4 sets of files:

1) The GDA toolbar <gda toolbar>  and events that occur when buttons on the toolbar are tapped are defined by XML and VBScript files GDA_1.0.apa and GDA_1.0.vbs. From left to right, icons when tapped effect the following:

  • Make station layer active (tap location on screen to add station). Drop-down menu item for plotting a station with bearing and distance from the currently selected station.

  • Add station at GPS location

  • Make geolines layer active (draw line on screen to add data). Drop-down menu item to draw a line with a polyline tool.

  • Make mylar layer active (draw line on screen to add data)

  • Show Edit toolbar

  • Show GDA Help

2) GDA modifies certain aspects of ArcPad's behavior with XML and VBScript files ArcPad.apx and ArcPad.vbs.

3) GDA help is provided by HTML help files in folder GDAHelp.

GDA help, Table of contents

4) GDA data for a mapping project reside in a single user-designated project directory. Multiple mapping projects require multiple project directories. Each project directory contains files for the 4 data layers described below, a collection of .dbf files that define picklists, per-station files of notes and sketches that may be created while using GDA, and an ArcPad.apm file (written by ArcPad each time work is saved) that defines active layers, pathnames, current map extent, and controls some symbolization. Empty copies of the data files are stored in a Templates directory that resides at the same directory level as the different project directories. A mapping project directory will also commonly contain a projection file, a subdirectory with base map layers, a subdirectory with compiled geologic data layers, and archive subdirectories.

GDA data structure

GDA adds 4 editable data layers to a project: stations, structure, geolines, and mylar. Most data layers have 5 files: 3 files with extensions shp, dbf, and shx that constitute a shapefile, an ArcPad XML layer-definition file with extension .apl, and--except for the mylar layer--a .vbs file that contains VBScript code called by events defined in the layer definition file.


Stations is the primary point data layer. Within it are recorded all station locations and much of the data associated with them. Adding a new station brings up an edit form that controls almost all point attributes and allows editing of associated tables for Samples, Photos, and the structure layer. Attributes of points in this layer are:

Unit page (see image)


Format (type, N bytes)

Editform label



Where is vocabulary defined?


Char, 16

Form caption

Station identifier

Generated automatically from Geologist, date, time



Char, 30


Geologic map unit (formal or informal, may be at any stratigraphic level)

Varies per project
Default is value at last station

Corresponding symbolization is defined in Stations_1.0.apl


Char, 10

Certainty of unit identification

Definite, probable, tentative



Char, 10

How located

How station is located

Inspection, Offset, Other
Set to GPS if location by GPS button



Char, 8

OC quality

Nature of outcrop

Good, poor, rubble, soil, none



Char, 5

OC min diam

Minimum diameter of outcrop

0.1m, 0.5m, 1m, 2m, 5m



Char, 8

Map scale 1:

Denominator of map scale at time station is located

Automatically generated



Char, 2


Used to calculate StationID




Char, 15

Not visible on form

If the current station was located by offset coordinates from another station, this field stores the ID of that 'datum' station.

Automatically generated


Lith page (see image)


Char, 100


Short lithologic description




Char, 10

Min grain size

Use to describe the minimum size of clasts, crystals, blasts, etc.

Udden-Wentworth scale.



Char, 10

Max grain size

Use to desctibe the maximum size of clasts, crystals, blasts, etc.

Udden-Wentworth scale.


The Lith page also has two buttons called ADD NOTE and ADD SKETCH which can be used to create and edit text or graphics files, respectively, related to the current station. For instance, when the ADD NOTE button is tapped during the attribution of a new station a file is created that is named with the station ID and given a .txt extension. The file is then opened with the first line consisting of the current date and time and you may add as much text as needed to describe the station or related attributes. During successive visits to the station, tapping the ADD NOTE button will open the original file and prepend the date and time of the visit.

The file extensions associated with these two buttons are .txt (ADD NOTE) and .psw (ADD SKETCH). By default, WinCE devices will use Pocket Notepad to open files with a .txt extension and Pocket Word to open those with a .psw extension. We chose Pocket Word for the sketch files only because it has a rudimentary drawing toolbar and it is available on all WinCE devices. There are a number of graphics programs designed for PDAs that will far exceed Pocket Word's drawing capabilities for a reasonable price. If you install one, you will need to change the GDA code so that the files created by the ADD SKETCH button are given an appropriate extension. Open Stations_1.0.vbs with a simple text editor such as Notepad and search for 'SketchPath' within the AddSketch subroutine. Change the string ".psw" to the extension associated with the graphics program you want to use. 

Other pages of the Stations form allow editing of subsidiary tables (dbf files) for Samples and Photos. Fields in these tables and the associated entries in the Stations edit form are shown in the tables below.

Sample page (see image)


Format (type, N bytes)

Editform label



Where is vocabulary stored?


Char, 16

not shown

ID of station at which the sample was collected.

Automatically generated



Char, 16

Listed in Samples from this station


Automatically generated



Char, 30


Type of analysis to be performed on sample



Photo page (see image)


Format (type, N bytes)

Editform label



Where is vocabulary stored?


Char, 16

not shown

ID of station at which the photo was taken.

Automatically generated



Char, 15

Listed in Photos from this station

With care, can match camera filename

Calculated from Prefix and No. Self-incrementing



Char, 100


Subject of photo

No pick list



Char, 8


Width of field of view

No pick list



Char, 5


View direction



With properly configured symbolization (see Symbolization), points in the Stations layer can be shown as dots whose color corresponds to MAPUNIT.


Structure is a point layer for storing and plotting orientation data (bedding, foliation, lineation, etc.) Such data are stored in a layer separate from the Stations layer so that they can be plotted. A point must first be added to the Stations layer before orientation measurements can be recorded. Structure data are added from the Str page of the Stations form (see image).

As each measurement is added to the Structure layer, GDA programmatically copies the coordinates of the station point to the Structure layer. Multiple structure measurements may be added at a single station.

Features of the Structure layer are described in the following table:


Format (type, N bytes)

Editform label



Where is vocabulary stored?


Char, 16

not shown

ID of station at which the structural observation was made.

Automatically generated



Char, 30



Corresponding symbolization is defined in Structure_1.0.apl


Char, 1

Poor observation (checkbox)

Unchecked (default)=F



Char, 3


Azimuth (strike, trend) in degrees, 0=North, clockwise
Follows right-hand rule: for N-S strike, AZI=0 for E dip, AZI=180 for W dip




Char, 3


Inclination (dip, plunge) in degrees, 0=horizontal, 90=vertical (down), -90=vertical (up)




Date, 8

not visible

Date of measurement.

System date


The table below shows the contents of StrucTypes_1.0.dbf as it is distributed in GDA. The Text field shows the value that will be stored within the STYPE field. Note that Structure_1.0.apl contains instructions for STYPEs in addition to those listed below; these can be added to StrucTypes_1.0.dbf and will be symbolized. Addition of other values to StrucTypes_1.0.dbf will require that you update the symbology defined in Structure_1.0.apl (see Symbolization). 


upright bedding

overturned bedding

bedding no top

bedding, horizontal









stretching L

mineral L

intersection L

foliation, horizontal


fold hinge


Geolines is a line layer for contacts, faults, shorelines, and other linear features. Attributes of lines in this layer and their characteristics are:


Format (type, N bytes)




Where is vocabulary stored?


Char, 24

Date and time of observation

Automatically generated



Char, 30


Geologic line type




Char, 20

Precision (m)

Precision of line location

1, 2, 5, 10, 25, 50, 100
default is 0, should be understood as NODATA



Char, 20

Map scale 1:

Denominator of map scale at which line is digitized

Automatically generated


The table below shows the contents of LineTypes_1.0.dbf as they are distributed GDA. The LINETYPE field shows the value that will be stored in the LTYPE field. If these values are changed or more are added and you wish to have new values symbolized properly, you will have to update the symbology (see Symbolization).




outcrop limit

scratch boundary

till bed

peat bed

ash bed.

bedding trace




marker bed





Mylar is a layer of unattributed lines, included to provide flexibility. Use Mylar for map ornamentation, text written directly on the map, or other annotation. Note that in most cases any information in this layer must later be translated into a form that can be queried by machine. 

Base map and compilation geology

ArcPad allows GDA to use a wide variety of base materials, including previous geologic data. The primary limitation is symbolization. Only one raster layer may be used at a time, as ArcPad does not support transparency.

Setup instructions.

Initial setup

Establish an ActiveSync connection between the PC and the PDA.
Install ArcPad on the PC:

Use the default installation folder suggested by the setup wizard, i.e. ‘ C:\Program Files\Arcpad’

On the PC, Start>Programs>ArcPad>Install ArcPad application for Windows CE
On the PC, Start>Programs>ArcPad>Install ArcPad font for Windows CE
On the PC, Start>Programs>ArcPad>Install VBScript Runtime Library for Windows CE

Install GDA:

Both the .bat and .cab files assume you installed ArcPad in the default directory!

Download the appropriate GDA package for your system and unzip the file.
For installation on the PC, double-click on GDA_PC_Install.bat.
For installation on the PDA, copy file to any folder, make a copy (.cab files disappear once unzipped), and double-tap the file.

Choose ‘No’ to any dialogs asking you to retry installation of a font file.

The default locations after installation are shown below. If you have chosen to install ArcPad in a non-default folder, you will have to move the files from the unzipped file manually.

Location on PC

Location on PDA

C:\Program Files\ArcPad\AppletFiles


\Program Files\ArcPad\Applets


C:\Program Files\ArcPad\SystemFiles


\Program Files\ArcPad\System


My Documents\GDAProjects\


\My Documents\





esri_7.ttf (ESRI Geology

After installation on a PC, move the My Documents\GDAProjects\Templates folder to another drive and folder if you wish; the other folders must remain within the ArcPad installation folder.

After installation on a PDA, move the My Documents\GDATemplates folder to a non-volatile storage card and make a copy of it for each project.

Configure PDA to communicate with Bluetooth GPS unit.

These are general instructions for making contact with a Socket Bluetooth GPS unit on an internally enabled bluetooth PDA. If you use a different GPS unit these instructions may not apply.

Make sure the GPS unit is fully charged.
Power on the GPS unit. The status LED will blink blue.
Power on the PDA.
Turn PDA Bluetooth radio ON (Tap blue and black icon in the lower right corner of PDA screen).
Tap Bluetooth icon (now blue and white) and open Bluetooth Manager.
Perfom a Bluetooth device discovery to find the GPS unit.
Pair and bond with the the Bluetooth GPS unit. Use the passkey 0183 if prompted. You only need to discover, bond with, and pair with the GPS unit the first time you use it with your PDA.
Start ArcPad and check the settings below before attempting to enable the GPS.

Configure ArcPad

Start ArcPad.

Open ArcPad Options (crossed wrench and hammer: top toolbar, 2nd icon from right, select Options...) and configure Protocol and GPS pages.

With the Socket GPS communicating via internal Bluetooth on an IPAQ H3900, appropriate settings are:

Protocol page

Protocol: NMEA 0183
GPS Datum: WGS84
Use Height in Datum Transform:
GPS Initialization String:

GPS page

Port: COM8
Baud: 4800
Parity: None
RTS Control: enable
DTR Control: enable
Infra Red:
Data Bits: 8
Stop Bits: 1
Monitor CTS:
Monitor DSR:
Show GPS Activity in System Tray:

IMPORTANT: On the Capture page enable averaging. 10 points is a good number. This is necessary for certain VB script routines to be fired properly, but it is also good GPS practice.

Configure other GPS quality parameters and warnings as needed on the Quality, Capture, and Alerts pages. For instance, you can tell ArcPad to reject any GPS fixes with a PDOP (position dilution of  precision) greater than 6 (4 is considered excellent and you may routinely see PDOP values better than 3. Never accept a PDOP greater than 8).

IMPORTANT: On the Paths page, set the Default Maps & Data Path to the project folder your data are in.

Save the map as ArcPad.apm within the default data folder. This map will now be opened by default when ArcPad is started.

Using GPS with ArcPad

Check that ArcPad is receiving valid NMEA strings by going to the GPS dropdown menu and choosing GPS Debug. If you see nothing, then something is configured incorrectly.
Always disable the GPS through ArcPad's GPS menu before you turn ArcPad off.
Likewise, disconnect the PDA from the GPS through the Bluetooth manager before turning the PDA off.
Failing to disconnect properly from the GPS will usually lock up the COM port which only a soft reboot will clear.

To start a new project

A mapping project has a common geographic area, a common geologic vocabulary, and a single map projection and datum. Many geologists will work on only one project. Others might have several, perhaps including a project mapping glacial deposits in western Washington in the Washington State Plane North feet-NAD83 coordinate system and a project mapping late Cenozoic rocks and deposits in northwest Oregon in the UTM10 meters-NAD27 coordinate system.

Directory structure

For each new project (new area, new projection, and (or) new theme), create a directory on your storage card by making a copy of Templates and renaming it to <NewProj>, where <NewProj> is a relatively short version of the project name. Within <NewProj>, create subdirectories for base layers and compilation geology as you see fit.. With two projects named BremE and Wen, the Storage Card directory tree would be :

\Storage Card\


files for geolines, mylar, stations, structure
Units_1.0.dbf, StrucTypes_1.0.dbf, etc.


files for geolines, mylar, stations, structure
Units_1.0.dbf, StrucTypes_1.0.dbf, etc.



ArcPad maintains a default data path (that is, a default directory). If a map-description file named ArcPad.apm is present in the default data path, that map will be opened when ArcPad is started.

Start ArcPad. Go to Tools>Options>Paths and change the default data path to your current map-project directory. Open a new map. Add base layers, Stations, Structure, Geolines, and Mylar to the map. Set the scales at which various layers plot, if you desire. Save the map--this will write an ArcPad.apm file to the map-project directory. ArcPad.apm defines the layers present in an map, the area shown on the display when the map is opened, and some symbolization.

You can re-save ArcPad.apm whenever you wish, and it may be useful to re-save before you exit ArcPad, though this is not necessary. It is best to overwrite the current version--don't Save As a new file.

Base materials

For convenience, keep all base materials in a subdirectory <NewProj>/Base. Possible base materials include:

  • Standard USGS DRGs

  • Shaded-relief images, calculated from standard USGS DEMs or high-resolution data

  • Orthophotos

  • Vector contours

  • Digital assessor's parcel maps

Note that only one raster file can be shown at a time, as ArcPad does not support transparent rasters. If you want to display a raster composite, for example colored unit polygons over shaded relief, you must explicitly create this image in ArcGIS and export it to a suitable image-file format.

Raster images must all be in the same projection. Convert vector layers to the same projection as well; ArcPad won't reproject on the fly.

MrSID compression is desirable, both to create image pyramids and to reduce overall file size. Experiment to find the appropriate degree of compression. We find 10-15x works well. The 50Mb limit for single files input to the MrSID converter in ArcGIS may require that some input files be chopped into smaller tiles.

Map projection

ArcPad needs to know the project map projection and the GPS cannot be enabled without one.

1) If you export the project from ArcGIS, a projection file (*.prj) should be created. Install this in the project directory.

2) You can put any prj.adf file (from within a coverage or grid – rename it to .prj) or .prj file (associated with a shapefile or from the ArcGIS\Coordinate Systems folder) into the project workspace. When you add a new layer that does not have an explicitly defined projection, you will be asked if you wish to use this projection.

3) You can assign a projection to each map layer with the Map Projection button (top right icon on the Layers dialog) in ArcPad.

ArcPad will not reproject data to a common projection  for a map project. All layers must have the same projection,.
All layers need not have a separately defined projection. Indeed, GDA takes advantage of this feature, and leaves the default geologic data layers with projections undefined, so that each new project may pick up its projection from an associated base layer or a freestanding projection file. 

Your choice of projection will usually be forced by the projection of the raster layers (DRGs, shaded-relief images, DOQQs) used for a map base.  In a given mapping project, such rasters should all be in the same projection.


You will need to edit Units_1.0.dbf to establish an initial unit vocabulary for a new project. Open a copy of this file in Excel, OpenOffice Calc, Access, or similar,  select and delete existing values, add new values, and re-arrange values. Note that "LITH" need not be specified. Save and move the modified copy of the file to the project workspace.

If symbolization is based on any vocabulary values you create or edit, you will need to change the symbology element within the shapefile’s .apl file. You may do this manually from within a text editor if you wish, but it is much easier to use the method outlined below. 


You can create symbology for a new project with ArcGIS or ArcView:

Included in the ArcPad install folder are two folders called apTools3 and apTools8. In these folders are extensions with export tools for use in either ArcView 3.x or ArcGIS 8.x (and 9.x).

To install apTools8.dll for ArcGIS:

  • Go to Start>Run and type: regsvr32 "C:\Program Files\ArcPad\apTools8\apTools8.dll" (or whatever the full pathname is to the file). Be sure you have administrator rights to your computer or the dll will not install properly.

  • In ArcMap, go to Tools>Customize

  • Click on the Commands tab and click on Add from file. Browse to apTools8.dll and select it.

  • Four commands will appear in the right-hand window. Drag Export Symbology to any toolbar.

To install apTools3.avx for ArcView 3.x:

  • Move all files in apTools3 to C:\ESRI\AV_GIS30\ARCVIEW\EXT32 (or the appropriate directory).

  • In ArcView, go to File>Extensions and turn the extension on.

Add the shapefile for which you want to create symbology to an ArcMap or ArcView map
Create a feature for every possible attribute and symbolize it.

Points can be symbolized with any true type font character, lines can be symbolized with different thicknesses and color only, and polygons can be symbolized with solid opaque colors only.

Click on the Export Symbology tool you just installed.
If you are setting the symbology for a point shapefile, open the .apl file for the shapefile that was just created and search for <TRUETYPEMARKERSYMBOL. Note the font being used for each occurrence of that XML element.
Drag and drop those fonts from your PC's fonts directory into the fonts directory on your PDA.

Rotating truetype symbols

To rotate point symbols according to an attribute value (eg Azimuth from the Structure shapefile):

Open the .apl file for the shapefile you are dealing with and search for VALUEMAPRENDERER.
Add these attributes to that XML element:

rotationfield="MYROTATIONFIELD" rotationtype="geographic"

Each time you start ArcPad

Each time you start ArcPad you will have to re-start communication between the PDA and GPS unit. With WinCE 3.0 and the Socket Bluetooth GPS,

Power on the GPS unit
Power on the PDA
Turn PDA Bluetooth radio ON (Tap blue and black icon in lower-right corner of PDA screen.)
Tap Bluetooth icon (now blue and white) and open Bluetooth Manager
Tap the entry for the GPS unit (EMTAC BTGPS 22..) to establish communication
Close Bluetooth Manager.

Once GDA is installed and the first map is saved as \Storage Card\<ProjName>\ArcPad.apm, ArcPad will restart with GDA up and running in the most recent project and map extent.

When we start GDA we routinely make GPS Active, enable GPS Tracklog, and--using the Layers form--make the GPS Tracklog invisible.

Data safety


Whenever you tap OK on the Station edit form, or tap ADD on the Structure, Photos, and Samples pages, data are written to memory. You need not tap the Save icon on the top toolbar.

The Save icon (or Save Map on the File menu) saves the current map extent, the list of map layers, and any special instructions you've defined with the Layers forms.  Tapping the Save icon every now and then doesn't hurt--and mostly isn't necessary.

Data not written to files

We have had problems with data not being written to dbf files. We think these problems have occurred because of mixed versions (e.g., an old .apl file and a newer .dbf format) or corrupt XML in a layer definition (.apl) file.

If GDA is properly configured and you pay attention, failure to record data will be evident immediately. (A) Set up Station point symbolization to reflect MAPUNIT. Are the dots the right color?  (B) Using the layer dialog, label each station point with MAPUNIT or the like. If you don't see MAPUNIT written beside a new station, data were not recorded. (C) Can you see structure symbols? If not, why? (D) Label each structure point with its INC.

If data are not written to dbf files, delete the feature and re-enter it. If data are still not saved, make paper notes.

If you find that data are not being written to dbf files, and particularly if you can establish the conditions that cause this to happen, please let us know.


At intervals, copy all data files to an archive folder, copy this folder to a PC, and burn it to CD-ROM for safekeeping. Data files include

Geolines_1.0.dbf, Geolines_1.0.shp, Geolines_1.0.shx
Mylar_1.0.dbf, Mylar_1.0.shp, Mylar_1.0.shx
Stations_1.0.dbf, Stations_1.0.shp, Stations_1.0.shx
Structure_1.0.dbf, Structure_1.0.shp, Structure_1.0.shx
Tracklog.dbf, Tracklog.shp, Tracklog.shx
all note (.txt) and sketch files
any projection files

It may be useful to put a copy of Units_1.0.dbf in the archive folder, to better understand the MAPUNIT and LITH vocabularies that were suggested to the mapper. It will also be useful to put copies of all digital photographs into the archive folder. We suggest naming the archive folder with the geologists' initials and date of archiving, (a truncated version of a station ID), such as 06_0322ET. The directory structure of the PDA storage card may then look like this:

/Storage Card/




Here are two strategies for archiving, each with its advantages and disadvantages: (1) You can COPY data files to the new archive folder. Grow a single, evolving set of data files for the project. Archive folders grow steadily larger and each archive folder supplants its predecessor. At any time, a single set of shapefiles encompasses all of the your data for the project. An advantage of this approach is that earlier observations are readily accessible.

(2) Or you can MOVE all current data files to the new archive folder. Replace them with blank shapefiles from the Templates directory. Keep the current Units_1.0.dbf. Move/copy appropriate photo files and note files to the archive folder. Data are not duplicated in multiple archive folders. An advantage of this approach is that database files remain small for better performance. A disadvantage is that several sets of archived shapefiles must be concatenated to capture the entire project.

Turn GDA databases into a narrative

The Python script (located in the Utilities folder) will turn a GDA project folder, or an archive folder, into a narrative in HTML format that is easily read, edited, and printed. Most computers with ArcGIS have Python available as part of the ArcGIS installation. To use this script you will have to locate and install modules dbf and image; see instructions within file

Incorporating GDA data into a desktop GIS

To move data into a desktop GIS, we have found it simplest to archive a project, then copy the entire archive directory to the computer that hosts the GIS. The archive directory on the PDA may then be deleted, or left for reference during further mapping. If the working directory on the PDA is on a storage card, you can temporarily mount the storage card on the GIS host for fast drag-and-drop transfer.

How GDA data are incorporated into a compilation project in the desktop GIS will depend strongly on the data structure of the desktop project. We suggest these guidelines:

  • Keep all GDA data in a "FieldData" directory within the compilation project workspace

  • Create a script for transferring data from archive subdirectories within the FieldData directory to the appropriate data layers in the compilation project. Think about how to avoid incorporating data from a single archive more than once!

  • We find it useful to incorporate almost all of the GDA Stations and Structure layers into the corresponding layers in the GIS compilation project. Geolines and mylar are used primarily as backdrops for digitizing linework in the compilation project.

  • Symbolize the stations layer in the GIS with dots the colored to match MapUnit. Plot (on screen or paper) these dots on top of unit-colored polygons from the units-contacts-faults compilation layer. This allows visual confirmation that the compiled geology matches field observations. One can also intersect the stations layer with units-contacts-faults polygons and search the resulting point coverage for mismatches.


We wrote GDA in the course of our employment with the U.S. Geological Survey. It is not subject to US copyright. You have an unrestricted right to modify and redistribute GDA code. However, we request that, as a matter of courtesy:

  1. If you redistribute GDA code, please include the file Copying.htm (in the folder Applets/GDAHelp/), with appropriate modifications.

  2. If you modify and redistribute GDA code, please retain notice of our authorship and identify your contributions.

  3. If you modify and redistribute GDA code, please rename all files (e.g., change the version number) and make corresponding changes to internal file references. This will minimize errors associated with mixing files from different versions of GDA. See Utilities/ for help.

  4. If you redistribute GDA code, with or without modifications, please allow others to freely modify and redistribute it also.

Customize with a DBF editor

During use--perhaps on a daily basis--you may find that Units_1.0.dbf should be edited for clarity and performance. We particularly find it useful to edit values in the LITH field, reduce the number of rows that correspond to differing values of LITH, and re-order rows. StrucTypes_1.0.dbf, SampType.dbf, and Geologists_1.0.dbf can be similarly edited.

Customize with ArcView or ArcGIS`

For new projects, and as projects evolve, symbolization will have to be created and modified. This can be done on a PC with ArcView or ArcGIS, and new symbology exported to layer definition (.apl) files that are then copied to the PDA. See Symbolization, above.

Customize by editing XML and VBS files with a text editor

All of GDA's behavior can be modified by editing the appropriate XML and VBS files. Use a text editor that works gracefully with plain ASCII, not Microsoft Word!  Modifying VBS files requires knowledge of VBS and a clear understanding of the internals of GDA. We don't recommend this for most GDA users.

Modifying XML files to change picklists, to change vocabularies from open to closed, and to modify some symbolization is relatively straightforward. Use existing XML as a guide to format. Copy, paste, and modify. Experiment! Be sure to keep an unmodified copy.  To test for corrupt XML, open the modified file with a browser such as Firefox (Microsoft's Internet Explorer 6 doesn't display XML). If the file will not display, it probably won't work.

Note that if you modify symbolization by directly editing the layer definition (.apl) file, the EXACT statements within VALUEMAPRENDERER must be in strict ASCII order, followed by a single OTHER statement. If the EXACT statements are not properly ordered, the symbolization will not work as you expect.

Customize using ArcPad Application Builder

If you wish to significantly modify forms, change or add attributes, or add new tables, we suggest working with ArcPad Application Builder. This is expensive. We found that the $1,500 cost of Application Builder is cheaper than the time required to learn VBScript and the innards of ArcPad. Expect to spend a lot of time reading ESRI's User Forums.

References Cited

Haugerud, R.A., and Thoms, E.E., 2004, Geologic Data Assistant (GDA): an ArcPad extension for geologic mapping , in Soller, D.R., editor, Digital Mapping Techniques '04: U.S. Geological Survey Open-File Report 04-1451,

For questions about the content of this report, contact Evan Thoms

Version history

Download a current version of Adobe Reader for free

| Help | PDF help | USGS Publications main page | Western Open-File Reports for 2006 |
| Privacy Statement | Disclaimer | Accessibility | Western Earth Surface Processes Team |

This report is available only on the Web

| Department of the Interior | U.S. Geological Survey |
URL of this page:
Maintained by: Michael Diggles
Date created: May 5, 2006
Last modified: May 5, 2006 (mfd)