Abstract:
This digital geospatial data set consists of outlines of the
study area in the report "Structure, Outcrop, and Subcrop
of the Bedrock Aquifers Along the Western Margin of the Denver Basin,
Colorado" (Robson and others, 1998).
Supplemental_Information:
Procedures_Used:
Study area outlines and tic marks were scanned from 1:50,000 maps
(Robson and others, 1998) at 200 to 800 dots per inch.
These scans then were saved into a TIFF (tagged image file format which
is a bit-mapped file format). The TIFF's were converted to unrectified
grids (ARC/INFO raster geospatial datasets), by the ARC/INFO command
IMAGEGRID. Vector geospatial data sets, known as coverages in ARC/INFO
terminology, were created from ascii files containing the latitude and
longitude coordinates in degrees, minutes and seconds. These coverages
were projected into a State Plane projection that was specific to each county
map. From these coverages, link files were then created to help register
the grids to the coverages by use of the ARC/INFO command CONTROLPOINTS.
Arc: controlpoints fig2_grid fig2_lin fig2_tics nominal identity # point
Registration root mean square errors of 0.005 or less were acceptable for
the creation of link files.
The unrectified grids were georectified with the ARC/INFO command
GRIDWARP, which transforms or rubber sheets a grid along a set of links
by using a first-order polynomial transformation. The grid-cell size
was resampled to a larger cell size to decrease processing time for
conversion to coverages.
GRID: setcell 20
GRID: fig2_20grid = fig2_rgrid
Line coverages were created from the georectified grids with the ARC/INFO
command GRIDLINE, using a line thickness of 150 feet, a weed tolerance
of 40 feet, and a default dangle of 0.7 times the thickness.
GRID: fig2_cov = gridline (fig2_20grid,positive,thin,nofilter,
round,noitem,150, #,40)
The coverages then were built with line and polygon topology.
To improve cartographic display, arcs
were smoothed by splining and generalizing in Arcedit with weed
tolerances ranging from 30 to 100 units.
Individual coverages containing the same thematic data were plotted
and checked for line accuracy and attribution. The individual coverages
were then appended to form a single thematic coverage.
The final coverage represents one thematic layer in
maps published in Robson and others (1998).
This data set is one of seven digital map data sets being published
for this area. The other six data sets are:
ARAPBASE - structure contours on base of upper Arapahoe aquifer
LFHBASE - structure contours on base of Laramie-Fox Hills
and Arapahoe aquifers
LFHTOP - structure contours on top of Laramie-Fox Hills aquifer
WELLS - location of wells
GEOSYMB - point and line geologic structure information
GEO - geohydrologic unit boundaries
Reviews_Applied_to_Data:
March 1998: Colleague review of 1:50,000-scale maps that
were generated from the original data set. Manuscript review
included validation of method as outlined in map report and
inspection for positional accuracy.
March 1998: Inspection of copy generated from this data set.
April 1998: Colleague review of original digital data set
and associated metadata. Metadata review included verification
of table and column/item identities and definitions, validation
of the reference data sets and citations, verification of
consistency between log file and documented procedures, and
validation of development method as described in the documentation.
References_Cited:
Robson, S.G., Van Slyke, George, and Graham, Glenn 1998,
Structure, outcrop, and subcrop of the
bedrock aquifers along the western margin of the Denver
Basin, Colorado: U.S. Geological Survey Hydrologic
Investigations Atlas HA-742, 5 sheets, scale 1:50,000.
Available through the internet at
<URL:http://rockyweb.cr.usgs.gov/frontrange/>