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Published 2006
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Digital Data Set of Orchards Where Arsenical Pesticides Were Likely Used in Clarke and Frederick Counties, Virginia, and Berkeley and Jefferson Counties, West Virginia

By Bradley W. Reed, Peter Larkins, and Gilpin R. Robinson, Jr.

Metadata
Spatial data set

Overview

This data set shows orchard locations in Clarke and Frederick Counties, Virginia, and Berkeley and Jefferson Counties, West Virginia where arsenical pesticides have likely been used. The orchard locations (fig. 1) were compiled from aerial photos and topographic maps for the time period of extensive use of arsenical pesticides between the 1920s and 1960s. An orchard's presence in this data set does not necessarily indicate the use of arsenical pesticides on that site or that elevated arsenic and metal concentrations are present. Arsenical pesticides may have been used on part, or none, of the land; furthermore, the land may have been remediated and may no longer contain elevated arsenic and metal concentrations in the soil.

Figure 1. Distribution of orchards in Clarke and Frederick Counties, Virginia, and Berkeley and Jefferson Counties, West Virginia, believed to have been under cultivation between the 1920s and 1960s when arsenical pesticides were likely used.

How These Data Were Created

The spatial database of orchard areas was compiled using twenty-seven USGS 7.5 minute series topographical maps covering Clarke and Frederick Counties, Virginia, and Berkeley and Jefferson Counties, West Virginia. Maps for each quad area were chosen based upon their publication date's proximity to the time period of extensive arsenical pesticide usage. The maps chosen were published between 1943 and 1972 and all have a scale of 1:24,000.

Orchard areas on the topographic maps were traced in order to aid in the digitization of the sites. The topographic maps were then scanned and geographically referenced using ERDAS Imagine version 8.7, turning them into rectified images using the 1983 North American Datum.

The USGS 7.5' series topographical maps used in this data set and their respective publication years used for the digitization of the orchards are as follows in table 1:

Table 1. List of 7.5' USGS topographic maps compiled for the purpose of digitizing orchard areas.

Note that the dates shown in table 1 are the publication dates of the topographic maps and that the survey for each area was performed prior to this date. The mosaic of the maps that were used can be seen in figure 2. Areas along the outer borders of the map having no topographic map shown were verified as having no orchards present, thus they were omitted from the mosaic to eliminate unnecessary processing time.

Figure 2. Orchards shown in relation to the mosaicked collection of topographic maps used to create the data set.

Orchard areas were digitized from the rectified topographic map images using ArcGIS version 9.1 to create the spatial database of orchards, which was then projected into the Universal Transverse Mercator Zone 18 North projection. Polygons were drawn according to topographic map and by county. This means that orchard areas that cross over either the topographic map or the county boundaries were split into separate parts. An example of this digitization method is shown in figure 3. Orchards were grouped by county in order to simplify the computation of spatial statistics by county location.

Figure 3. Orchards digitized using 7.5' USGS topographic maps as a guide. The expanded section shows how orchards were digitized by county boundaries, with orchards that cross being divided into separate entities.

The orchard data set includes several descriptive attributes that identify each orchard's polygon (table 2). The values for area of the polygons were calculated using the XTools Pro version 3 extension for ArcGIS desktop.

Table 2. Descriptions of attributes in the Orchard digital data set.

Limitations of the Data Set

The spatial accuracy of the orchard polygons is limited to the scale of the 7.5' topographical maps used to digitize them. All of the topographical maps used for this study had a scale of 1:24,000. The topographic maps used meet National Map Accuracy Standards with a spatial accuracy of ±40 feet. Since the orchards were digitized from these maps after they were scanned and georeferenced, a second level of error was introduced. For this reason, spatial accuracy is considered to be ±60 feet.

About the Files in this Digital Publication

This digital data set is available on the World Wide Web at URL http://pubs.usgs.gov/of/2006/1330/shapefile/ as an ArcView shape file. The metadata (documentation) of the orchard data set is available at the same location. The metadata provides detailed information on data quality, spatial-data organization, spatial reference, spatial entities and attributes, and other aspects of the data set. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Some of the spatial reference attributes of the data set are as follows:

Projection: Universal Transverse Mercator (UTM) Zone 18
Horizontal Datum: North American Datum of 1983
Spheroid: Geodetic Reference System 80
Central Meridian Reference: -75 degrees
Horizontal Units: meters
False Easting: 500,000 m
False Northing: 0 m

ArcView files can be viewed with the free viewer, ArcExplorer, which can be downloaded from http://www.esri.com/software/arcexplorer/.