U.S. GEOLOGICAL SURVEY DIGITAL 
RASTER GRAPHICS 
Laurence R. Moore, William A. Kunert 
U.S. Geological Survey 
1400 Independence Rd., Rolla, Missouri, USA 
ABSTRACT 
A digital raster graphic (DRG) is a raster image of a published map. The U.S. Geological 
Survey plans to produce DRG’s of its standard topographic map series through contracts 
with the private sector and through partnerships with State agencies. 
DRG's are made by scanning published paper maps on high-resolution scanners. The 
raster image is georeferenced and fit to the UTM grid. Colors are standardized to remove 
scanner dependencies and artifacts. The final data set is about 10 megabytes in Tagged 
Image File Format (TIFF) with packbit compression. DRG’s can be easily combined with 
other digital cartographic products, such as digital elevation models and digital ortho- 
photoquads. Using DRG’s and derivative products as source material makes vector data 
collection and revision faster, cheaper, and more accurate than traditional methods. DRG's 
provide a spatially accurate, visually appealing backdrop for other geographic data. A 
DRG combined with a digital orthophotoquad image can be used for monoscopic vector 
collection and revision. The combined image significantly reduces total collection and 
revision times. DRG's can provide inexpensive, consistent base data for the entire country. 
1. INTRODUCTION 1.1 Raster Graphics in Cartography 
Digital raster maps are not new. Some of 
images of published maps. A DRG can be the earliest digital maps were simple raster 
thought of as a picture of a map taken images made with text symbols on line 
with an electronic scanner instead of a film printers. Such maps were not very useful. 
camera. They had low resolution, were not visually 
appealing, and were not useful for 
automated land analysis. 
Digital raster graphics (DRG) are digital 
Unlike most vector representations of 
maps, DRG's do not attempt to alter or 
enhance the cartographic content of a 
map. DRG's exactly duplicate the map's solved several of these problems. Vector 
cartographic content on a different maps could hold large amounts of useful 
medium. information, yet still be small enough to be 
manipulated by the computers of the 
1970's and 1980's. Digital cartography 
through these years, therefore, emphasized 
vector data. 
Digital maps based on vector models 
Any use of trade, product, or firm names is 
for descriptive purposes only and does not 
imply endorsement by the U.S. 
Government. By the late 1980's, computer visualization 
technology had nearly caught up with 
cartographic requirements. Interest in 
raster images of maps began to grow again 
26 
as computer: 
map images 
and affordat 
Today, desk 
powerful en 
images of la 
information 
vector and r 
1.2 Backgro 
Product 
Various Fed 
mented with 
different kin 
few years. S 
similar prodi 
The U.S. Ge 
proposed a « 
for USGS st 
1994. The p 
graphic was 
cartographic 
adopted this 
confusion by 
Through the 
produced a 1 
1:24,000-sca] 
These test m 
strations to « 
government 
refine the re 
product. 
In October 1 
Report" on c 
memory (CD 
public. This 
from the use 
The CD con 
USGS quadr. 
and 1:250,0C 
mentation, n 
derivative pr