A digital raster graphic (DRG) is a scanned image of a U.S. Geological Survey (USGS) standard series topographic map, including all map collar information (Collared). The image inside the map neatline is georeferenced to the surface of the earth and fit to the Universal Transverse Mercator (UTM) projection. The datum is NAD 83 and the UTM Zone is 15 for Arkansas. The horizontal positional accuracy and datum of the DRG matches the accuracy and datum of the source map. The map is scanned at a minimum resolution of 250 dots per inch. This gives an approximate cell size of 2.4 meters for the 1:24,000 DRGs. The units of the DRGs are meters. DRGs can be purchased from the USGS or obtained free online for Arkansas at this web site.
Projection: The Universal Transverse Mercator Grid
 |
| Figure 1. The Universal Transverse Mercator grid that covers the conterminous 48 United States comprises 10 zones—from Zone 10 on the west coast through Zone 19 in New England. |
The National Imagery and Mapping Agency (NIMA) (formerly the Defense Mapping Agency) adopted a special grid for military use throughout the world called the Universal Transverse Mercator (UTM) grid. In this grid, the world is divided into 60 north-south zones, each covering a strip 6° wide in longitude. These zones are numbered consecutively beginning with Zone 1, between 180° and 174° west longitude, and progressing eastward to Zone 60, between 174° and 180° east longitude. Thus, the conterminous 48 States are covered by 10 zones, from Zone 10 on the west coast through Zone 19 in New England (Fig. 1). In each zone, coordinates are measured north and east in meters. (One meter equals 39.37 inches, or slightly more than 1 yard.) The northing values are measured continuously from zero at the Equator, in a northerly direction. To avoid negative numbers for locations south of the Equator, NIMA's cartographers assigned the Equator an arbitrary false northing value of 10,000,000 meters. A central meridian through the middle of each 6° zone is assigned an easting value of 500,000 meters. Grid values to the west of this central meridian are less than 500,000; to the east, more than 500,000. (USGS Fact Sheet 077-01, August 2001) All the DRGs in the NSDD are in the UTM NAD 83 Zone 15 coordinate system. The NSDD DRG images can be reprojected to any coordinate system using the free ERDAS ViewFinder software listed below under tools.
Descriptions:
Digital Raster Graphics (DRGs) are digitized color USGS topographic maps. The
NSDD DRGs are geo-referenced tiff (*.tif) and MrSID (*.sid) files, available in three versions:
collared, seamless, and collarless hillshaded at the 1:24,000 scale, collared
and seamless at the 1:100,000 scale, and collared and seamless at the 1:250,000
scale .
Collared DRGs include the map border, marginalia, and legends. Seamless DRGs do
not have collars and can be tiled together so you can create a seamless mosaic
view of an area. The collarless hillshaded DRGs are hillshaded using the
National Elevation Dataset (NED). The NED is a raster product
assembled by the U.S. Geological Survey. NED is designed to provide National
elevation data in a seamless form with a consistent datum, elevation unit, and
projection. Data corrections were made in the NED assembly process to minimize
artifacts, perform edge matching, and fill sliver areas of missing data. NED has
a resolution of one arc-second (approximately 30 meters) for the continuous
United States, Hawaii, Puerto Rico and Virgin Islands. They are the same
resolution as the 1:24,000 collarless DRGs, which has an approximate cell size
of 2.4 meters, but hillshaded to give the maps a three-dimensional perspective.
The collarless hillshade DRGs were created using a sequence of programs
developed by Robert Weih.
Data
Resolution
DRGs made before October 2001 have scan resolutions of 250 dots per inch
(dpi). Most DRGs made after October 2001 have scan resolutions of 500 dpi. The
ground resolution of the image is directly related to map scale. For 250 dpi
images, this relationship is:
| Map Scale | DRG ground resolution |
| 1:24,000 | 8 ft = 2.438 meters |
| 1:100,000 | 33.33 ft = 10.16 meters |
| 1:250,000 | 83.33 ft = 25.4 meters |
Both the scan and the ground resolutions of a DRG are simply measures of pixel size. Unlike a digital aerial photograph, the resolution of a DRG is not a measure of the detail that can be seen on the map.
DRG
Publication Date
Shown below is the date the 1:24,000 USGS Quadrangle Maps were published for
Arkansas.
| Published Date | Percentage of Quadrangles |
| 1950 - 1959 | 2.3% |
| 1960 - 1969 | 18.8% |
| 1970 - 1979 | 41.3% |
| 1980 - 2003 | 37.6% |
Data File Types
All NSDD DRGs are in Zip (*.zip) format. The name of the files are the same
as the USGS map sheet. If you do not have a zip utility, you can follow this link to download one
Here. The following information will give you more
detail on the DRG and their associate files.
The NSDD DRGs are in either the Tagged Image
File Format (TIFF) or the Multi-resolution Seamless Image Database (MrSID)
file format. MrSID is a high-quality, high-performance wavelet based lossy
compression methodology designed specifically to enable true portability of
massive images. The MrSID Encoder is developed and supported by LizardTech,
Inc. Many remote sensing and Geographic Information System (GIS) support
the MrSID file format. If they don't support the MrSID format, you can use
a free software package (MrSIDViewer) to export the MrSID file, or a subset of
the image file, into the TIFF file format.
| DRG Type | File Type | Included Files | Approximate *.zip File Size |
| 1:24,000 Collared | GEO TIFF | *.tif, *.tfw | 3 MB |
| 1:24,000 Collarless | GEO TIFF | *.tif, *.tfw, | |
| 1:24,000 Collarless Hillshaded | MrSID 15:1 | *.aux, *.sid, *.sdw | 10 MB |
| 1:100,000 Collared | GEO TIFF | *.tif, *.tfw | 6 MB |
| 1:100,000 Collarless | GEO TIFF | *.tif, *.tfw | |
| 1:250,000 Collared | GEO TIFF | *.tif, *.tfw | 5 MB |
| 1:250,000 Collarless | GEO TIFF | *.tif, *.tfw |
World File (Coordinate Information)
All the NSDD DRGs have World files (*.tfw for TIFF files and *.sdw for MrSID files). They have been included as a service to users of ESRI software and other commercial software that uses ESRI's world files. The world file contains the ground coordinates of the upper left pixel of the TIFF image (the (1,1) or (0,0) pixel, depending on convention), and scale and rotation information. World files do not contain projection and datum information. More information about world files can be found at http://support.esri.com.
AUX File (Projection and Datum Information)
An Auxiliary file (.aux) is a file that accompanies the raster in the same location and stores any auxiliary information that cannot be stored in the raster file itself. This is where statistical information for the raster dataset will be stored, if it cannot be stored internally. Color map, histogram/table, coordinate system, transformation, and projection information may also be stored in the AUX file. The information stored in an AUX file is only accessible using a product from ESRI®, ERDAS or a third-party product derived from their products. All the NSDD DRGs have an *.aux file association with them that stores the projection information of the DRG.
RRD File (Pyramid Layer)
The Pyramid layer (*.rrd) is a file that we have created for all tiff DRGs in the NSDD. This file speeds up the drawing of a tiff when using a product from ESRI®, ERDAS or a third-party product derived from their products. The amount of detail you see when drawing a raster data layer (DRGs, scanned photograph, etc.) depends on its cell or pixel size. If each cell covers a very small area so that details are maintained, then more cells are required to cover the same area; more detailed raster data require more space on disk and also takes longer to draw. To speed up the display of large raster images, we created pyramid layers, in which the original data has several levels of resolution. With pyramids, a lower resolution copy of the data displays quickly when drawing the entire dataset. As you zoom in, levels with finer resolutions are drawn; performance is maintained because you're drawing successively smaller areas. Without pyramids, the entire raster dataset must be queried to determine the subset of cells that need to be displayed. Pyramid layers provide a significant improvement in drawing performance.
Forestry GIS (fGIS)
Forestry GIS (fGIS™) is a Freeware Mapping Utility for
Resource Managers and a compact shapefile editing program, digitizer and GIS
data query tool for Windows®. Designed for operational field managers like
foresters and wildlife biologists, fGIS has essential tools tailored for
precision mapping on a desktop computer. Use fGIS to customize layered views
including aerial photos and other imagery, draw map objects, query and search
spatial data, annotate maps for printing, and much more. The standalone program
is unlimited, producing shapefiles and geo-referenced images compatible with
commercial software in an enterprise GIS framework. Forestry GIS is meant to be
part of a hierarchy of GIS tools, with ArcView/ArcGIS being the WI DNR standard
for advanced GIS users.
Forestry GIS (fGIS™) can be downloaded from the following link:
http://www.digitalgrove.net/fgis.htm.
Updates to fGIS are posted regularly at this link, so it's a good idea to check
back often.
You'll find that fGIS is relatively simple to use:
* Open and view geo-referenced raster images including digital orthophotos and
topographic maps in MrSID®, ECW, BIL, JPG, TIFF, GeoTIFF, BMP and PNG file
formats.
* Open and view vector data in ESRI® shapefile (SHP) and e00 files, AutoCAD DXF™,
MapInfo® MIF, Microstation® DGN, DLG-O, TIGER2000/line and TatukGIS SQL (ttkls)
file formats. An advanced R-Tree index system allows easy viewing of large (100+
MB) data files.
* Create and edit point, line and area shapefile objects and their associated
data attribute tables.
* Designate the direction and distance of the next leg of a line or polygon with
the COGO-like Traverse Tool. Directions can be entered in decimal degrees or
degrees-minutes-seconds (handy for plotting deeds or laying out a field data
collection route).
* Split a polygon into smaller units by drawing a line with the Split Shapes
Tool. Area and perimeter attributes of forest cover type subunits are
automatically updated.
* Customize map properties including line width and color, area fills, label
fonts and positions, image transparency, thematic rendering of data and more.
* Measure areas and distances. fGIS reports distances and areas in English units
(feet, miles and acres) and metric units.
* Display data at user-specified scales.
* Extract geo-referenced images of selected portions of a screen display.
* Export part of a vector layer and save it as a new file.
* Manage large data sets organized in dBase tables with the "Load Library Layer"
utility.
* Join dBase and Access tables to shapefile attribute tables.
* Create point shapefiles from comma delimited text files with x|y coordinates.
* Print the map with three flexible output options. The Simple Print command
will add a map title, subtitle, footer and the scale to the page. The Send Map
to Word command will send an image of the view at a user specified resolution
and scale to Microsoft® Word. A third option through the Export Image tool will
send the map to a technical illustration/page layout module called Diagram
Designer. You can add headers, legends, annotations and non-spatial symbols from
template palettes in the Diagram Designer module.
Zip Utility
All NSDD DRGs are in .zip format.
If you do not have a zip utility, you can download the file.
DLGV32Pro
From the USGS site, a free
viewer, DLGV32PRO can be downloaded to view files such
as *.tif, *.drg, and *.dem.
MrSIDViewer The
free MrSID Viewer is licensed from International Land Systems, Inc. and is a
cooperative product with Lizardtech, Inc. ILS can be reached over the Internet
at http://www.landsystems.com. The MrSID
Viewer displays images that have been compressed into the MrSID format.
Currently, the MrSID Viewer is available for Windows 95/NT, IRIX 6.2, Linux
2.0.32 and Solaris 2.5.1. The MrSID Viewer can be download from
Lizardtech, Inc. (Version: 2.0.0.50).
ERDAS
ViewFinder 2.1 ERDAS ViewFinder is a
free viewing tool provided by Leica Geosystems' GIS & Mapping
Division. It provides basic image viewing and manipulation capabilities,
including the ability to: The ERDAS ViewFinder can
be download from ERDAS.
DRG-Tools
(v3.7)
This ArcView 3.x extension provides specific
utilities for use with most digital raster graphic (DRG) images. A DRG is a
scanned image of a USGS standard series topographic map. For more information
about DRG products and ordering, visit the DRG Program home page at:
http://mcmcweb.er.usgs.gov/drg/
The current DRG-Tools extension provides these options:
An archive of DRG-related *.clr, *.avl, and *.avp
files is also included.... the complete description can be found in the
readme.txt file included in the zipfile.
Image-Tools (v2.6)
This ArcView 3.x extension provides various
image-related utilities, including specific features for use with single-band
images (such as topographic map scans, DRG, DOQ, NOAA chart, and other
pseudocolor/color-indexed products) as well as multi-band images (such as true
color airphotos). The current Image-Tools extension provides these
options:
* Side by side single-band image viewing (edgematching
- making overlap transparent). * Note: Spatial Analyst is
NOT REQUIRED to use the core features of the extension. Once downloaded and
unzipped, please read the file "imgtools.txt" for further
information.
The SAL has created a lesson (PDF format) that explains how to subset a MrSID
image and export it as a TIFF Image file.
*Display ERDAS IMAGINE *.img, *.tif,
and *.sid image files.
*Overlay, smooth, sharpen, enhance,
and reproject multiple images on-the-fly.
*Reproject imagery from its existing
projection system to one of many predefined output datums and
projections, creating files in either the IMG or GeoTIFF formats.
* Side by side DRG image viewing (edgematching - making the collar
transparent).
* Isolate particular DRG image features, such as contours or hydrography.
* Toggle DRG image colors to/from transparent.
* Display DRG image colors in grayscale.
* Restore default DRG image colors.
* Display transparent DRG colors as white.
* Save a colormap file for the active DRG image (including transparent
colors).
* Load a colormap file for DRG images (including transparent colors).
* Make all DRG images visible. * Activate (highlight) all DRG images.
* Build an image catalog from DRG images in the view.
* Convert active DRG images to grids (transfers DRG colors to grid theme).
* Note: Spatial Analyst is NOT REQUIRED to use the core features of the
extension.
* Isolate particular single-band image colors.
* Toggle single-band image colors to transparent.
* Display single-band image colors in grayscale.
* Restore default image colors.
* Display transparent single-band image colors as white.
* Save a colormap file for the active single-band image (including transparent
colors).
* Load a colormap file for single-band images (including transparent
colors).
* Make all images visible (or all single-band images or all multi-band
images).
* Activate (highlight) all images (or all single-band images or all multi-band
images).
* Build an image catalog from images in the view.
* Build an image catalog from images stored on disk.
* Export views to georeferenced JPEG images (with quality and DPI
settings).
* Convert active single-band images to grids (transfers image colors to grid
theme).