Delaware State DRG and DLG Server Homepage

PLEASE SELECT A COUNTY BY MOVING YOUR CURSOR OVER THE MAP OF DELAWARE ON THE RIGHT.

DLGs - Digital Line Graphs produced by the United States Geological Survey. DLGs consist of several layers of 1:24,000 map scale (vector) data for each USGS defined quad: boundaries, hydrography, vegetative surface cover, non-vegetative features, roads and trails, railroads, pipe and trans lines, and manmade features. Also included in this dataset is a hypsography (elevation contour) layer, nine layers in all. Data are projected in UTM coordinates using datum NAD83.

DRGs - Digital Raster Graphics produced by the United States Geological Survey. DRGs are scanned (raster) images of the USGS Topographic Sheets. They are most commonly used as basemaps for georeferencing other datasets or for visual analysis. DRGs are available at 1:24,000 (quad level, 7.5 min. series), 1:100,000 (30 x 60 min. series), and 1:250,000 (1 x 2 degree series) map scale. These data are also projected in UTM coordinates using datum NAD83.

DLG and DRG data are available at the quad level and can be accessed by clicking on the map to the right. Smaller spatial scale data is available in DRG format only and can be obtained through Delaware Region Small-Scale Series DRGs

If you are interested in a particular geographic feature but are unsure which quad contains that feature, try searching the USGS Geographic Names Information Server (GNIS).

Notes on File Fomats:

Due to the large amount of data involved, data files for each quad are archived and compressed into a single zip file for easy downloading. Each file format has its own zip file. Therefore, there are five zip files available for each quad: four formats for the DLGs and one for the DRGs (see below). Zip files were created using the Windows utility WinZip 7.0 under normal compression. If you do not have access to WinZip software, you can download a trial version or purchase the full program from the WinZip Homepage. Unix users may extract and uncompress "winzipped" files using the unzip command. Check here for additional notes on the file naming convention.

DLGs

Digital Line Graphs are available in the following four data formats: USGS DLG Standard, USGS DLG Optional, Arc/Info Export files, and ArcView Shapefiles. USGS DLG Standard (.dd) and Optional (.do) data are contained in ASCII files and well documented in the metadata file (.cns) included with each zip file and in the USGS DLG Standards. Here is a list of differences between Optional and Standard formats. An additional brief readme file is available for the hypsography-only data.

All Arc/Info Export (.e00) files and ArcView Shapefiles (.shp, .shx, .dbf) were created from the DLG standard format data. The DLGARC command with all default options was used in Unix Arc/Info Version 7.2.1 for this procedure. These files should be readable by most versions of Arc/Info and ArcView on Mac, Windows, and Unix operating systems.

DRGs

Digital Raster Graphics (DRGs) are available in TIFF 6.0 format only. Each DRG comes with the image file (.tif), the projection/world file (.tfw), and the metadata data file (.cns). The last two files are in ASCII format. A separate GIF (.gif) file is also available for 1:100,00 and 1:250,00 map scale DRGs. (These gif files should be used for visual purposes only.)

DLG Production

As mentioned above, the Delaware Digital Line Graphs (DLGs) are made up of several layers of 1:24,000 map scale (vector) data for each Delaware USGS topographic quadrangle. These DLGs were produced through an Innovative Partnership between the Delaware Geological Survey and GeoDigital Mapping, Inc. in Sterling, Virginia and supported by the General Assembly. The final digital layers were also provided to the USGS for inclusion in the National Digital Database. The layers were collected from the 1992-93 complete revision topographic maps, a product of a 5-year co-operative mapping program with the USGS. The layers include transportation, hydrography, boundaries, vegetative cover, non-vegetative cover, and manmade structures. These layers plus the hypsography layer collected in 1993-94 make a complete DLG package for the Delaware topographic quads. More detailed information can be found in the metadata file included with each downloaded data file.

Delaware is the only state in the nation to boast complete and up-to-date topographic coverage in analog and digital maps. All the DLG layers are also available on CDs that can be borrowed from the Delaware Geological Survey Earth Science Information Center by contacting W.S. Schenck at rockman@udel.edu.

DRG Production

DRGs were produced solely by the United States Geological Survey. RDMS and DGS obtained these data from USGS via CD-ROMs. For detailed information on the process for scanning the topo sheets, see the metadata file included with the data download or the USGS DRG Factsheet.

For Additional Information:

For more general information on DRGs and DLGs and information concerning file formats and specifications, please see the RDMS Data Frequently Asked Questions (FAQ) Page. For detailed information about the data content, including descriptions of major/minor attribute codes of DLG data, see the USGS National Mapping Program Geospatial Standards.

If you are interested in obtaining Digital Elevation Models (DEMs) or Digital Ortho-photo Quarter-Quads (DOQQs) for the State of Delaware, the data is available online at the Spatial Analysis Lab, College of Agriculture and Natural Resources, University of Delaware.

If you have further comments or questions, please contact RDMS or the Delaware Geological Survey.