1
THE U.S. GEOLOGICAL SURVEY’S REVISION PROGRAM FOR
7.5-MINUTE TOPOGRAPHIC MAPS
Larry Moore, lmoore@usgs.gov
U.S. Geological Survey, Mid-Continent Mapping Center
Rolla, Missouri
December 2000
ABSTRACT
From the mid-1940’s through the late 1980’s the 1:24,000-scale, 7.5-minute topographic
quadrangle was the primary product of the U.S. Geological Survey’s (USGS) National Mapping
Program (NMP). This map series includes about 53,000 map sheets for the conterminous United
States and is the only uniform map series that covers this area at such a large scale. The
7.5-minute mapping program lasted almost 50 years, from the mid-1940’s until the early 1990’s.
Revision programs that date from the late 1960’s have kept the median currentness date of the map
series at 1979.
There are four main categories of map revision: minor, basic, complete, and single edition. Minor
revision is done on maps that have few changes since the last revision; it includes boundary
updates and corrections of previously reported errors. Basic revision updates features from digital
orthophoto quadrangles (DOQ) and aerial photographs. Complete revision of all layers is seldom
performed because of the high cost. Single-edition revisions are done by the U.S. Department of
Agriculture Forest Service using procedures similar to basic revision. Contour update is an
optional part of basic and single edition revision but is not often done because of the high cost.
These revision programs were not designed to do replacement mapping. Most map revision is
done from remote and secondary data sources, including the following:
• Geometry is controlled and some feature content interpreted from DOQ’s.
• Most feature content is interpreted by using stereophotographs from the National Aerial
Photography Program.
• Boundary and name information is collected from Federal databases, other maps, and State
and local agencies.
During the height of the 7.5-minute mapping program, a large part of the NMP budget was focused on
graphic mapping. Because of funding increases in areas outside graphic map production and evolving
customer priorities, the NMP today spends more of its data production resources on digital and image
products, as well as more money on geographic research, data distribution, and customer assistance.
Because of the expense of traditional topographic mapping, the NMP is investigating alternate data sources,
procedures, and product designs for graphic maps.
INTRODUCTION
In 1989, the Mapping Science Committee of the National Research Council wrote that "...the primary product [of the
U.S. Geological Survey (USGS) National Mapping Program (NMP)] is the 1:24,000, 7.5-minute topographic
quadrangle series. This...is the only uniform map series that covers the entire area of the [continental] United States
in considerable detail. The series will be completed in 1990...NMP's principal raison d'etre is changing to the
equally challenging task of maintaining currency of these maps...A major ongoing revision effort, which the NMP is
now pursuing, is required" (National Research Council, 1990, p. 8).
The USGS produces printed maps and digital map data for all States, possessions, and territories of the United
States, and Antarctica. This paper discusses only the 1:24,000- and 1:25,000-scale topographic maps in the 48
[January 2003. This paper was written in late 2000. The USGS has since announced The National Map, a program
designed to create "...a seamless, continuously maintained set of public domain geographic base information that
will serve as a foundation for integrating, sharing, and using other data easily and consistently." For more
information, see The National Map Web site at www.nationalmap.usgs.gov]
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continental United States. There are 54,890 standard 7.5-minute and 7.5- by15-minute cells in this domain.
Because the two cell sizes overlap, the number of map sheets has varied with time. At present, there are 53,336 map
sheets that cover the continental United States. Both cell sizes and scales are referred to in this paper as "7.5-minute
maps" or "7.5-minute quadrangles."
The 7.5-minute maps are more detailed versions of other quadrangle series that date back to the formation of the
USGS in 1879 (Schwartz, 1980, p. 311). Although 7.5-minute maps were produced by the USGS as early as 1908,
the effort to cover the country at this scale was a product of World War II technological advances and 1939
legislation creating a National Mapping Program (Bohme, 1989, p. 167). Initial coverage of 7.5-minute maps in the
continental United States is summarized in figure 1. The program grew rapidly from 1945 through 1955, then more
slowly, and peaked in 1973. In the early 1980’s, it became evident that production rates were not sufficient to finish
the series before the year 2000. Beginning in 1982, manuscript maps without final cartographic finishing were
published (Bohme, 1989, p. 167). These were designated "provisional maps" (P-maps). A significant production
increase in the mid-1980’s resulted from the lower cost of provisional mapping (fig. 1). Most of the work on the
7.5-minute maps was finished by 1990, and the series was officially declared complete in 1992.
MAP REVISION PROGRAMS
7.5-minute maps have been revised almost from the beginning of the program, but revision numbers did not become
significant until the mid-1960’s (fig. 2). To speed up the revision of existing map sheets, an interim revision was
introduced in 1967 (Bohme, 1989, p. 167). Commonly called photorevision, this remained the most common type
of revision through the 1980’s. The original map base was used as horizontal control, and new features were
collected from stereophotographs without field verification. Contours usually were not revised. To show that the
Figure 1. Original production of 7.5-minute quadrangles. Each data point is the number of quadrangles
published in a particular year. Each cell is shown only once, the first time a map for the cell was made. The
median date of printing is 1972. The smooth gray curve is a polynomial trendline.
The data for this and the other figures in this report are from National Mapping Program databases, including
the map catalog (MAPCAT) and the assignment management system (AMS).
0
500
1000
1500
2000
2500
3000
1930 1940 1950 1960 1970 1980 1990 2000
Date of map printing
Number of quadrangles
3
revision did not meet new mapping standards for control and field verification, new photorevised features were
printed on the maps in purple.
With the completion of the 7.5-minute mapping program in 1992, the USGS began formulating a graphic revision
plan to keep primary series maps current. Decisions about revising 7.5-minute quadrangles are based on user
requirements, available resources, and the preferences of funding cooperators. Accuracy assessments, evaluations of
existing quadrangle materials, and error reports are also considered. For the last several years, the two primary
drivers of the NMP revision program have been the following:
• Cooperative funding from other agencies. The USGS will divide revision costs equally with other State or
Federal agencies.
• A list of 5,000 "high seller" maps. These maps are judged to be most in demand and are given priority for
revision work. A percentage of these maps are revised each year with or without cooperative funding.
Other criteria, such as less formal input from other State and Federal agencies, are also considered. Revision
decisions are also constrained by data availability, especially of recent aerial photography and digital orthophoto
quadrangles (DOQ) for the quadrangle under consideration.
Age of the 7.5-Minute Series
Figure 2 shows the overall currentness of the 7.5-minute maps at the end of 1999. The median currentness date for
the series as a whole is 1979, so the average 7.5-minute map is almost exactly 20 years old. The data in this figure
Figure 2. Currentness of revised maps compared to original maps. The solid line shows the date of source
materials (date of aerial photography in most cases) for the data set in figure 1. The dashed line shows the date
of source for the most recent revision of each cell. For example, 1981 is the source photography date for the
most recent revision of about 3,000 quadrangles. The median currentness date for original mapping is 1966; the
median for latest revisions is 1979. The data include minor revisions but not maps reprinted "as is" to replace
low shelf stock.
0
500
1000
1500
2000
2500
3000
3500
1930 1940 1950 1960 1970 1980 1990 2000
Date of map source materials
Number of quadrangles per year
Original mapping
Latest revision
4
include all photorevisions and minor revisions but not maps reprinted "as is" to replace low shelf stock. Aerial
photographs and other source materials used for map revision are usually 3 to 5 years old by the time the map is
published, so most maps printed in 1999 appear in the years 1994 to 1996 in figure 2.
Figures 3 and 4 show the geographic distribution of the oldest and youngest maps. 9,270 maps have currentness
dates of 1970 or earlier (fig. 3), and about the same number (9,420) are current as of 1990 or later (fig. 4). The
remaining 34,650 quadrangles were made or revised between 1971 and 1989.
Many of the oldest maps are in relatively isolated areas with low populations and low land values. These areas may
have experienced very little change since the maps were originally compiled.
Figure 3. Oldest maps.
Locations of the 7.5-minute
quadrangles with currentness
dates of 1970 and earlier.
9,270 quadrangles are
shown.
Figure 4. Newest maps.
Locations of the 7.5-minute
qudrangles with currentness
dates of 1990 and later.
9,420 quadrangles are
shown.
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Types of Revision
There are currently four official types of map revision: minor revision, basic revision, complete revision, and
single-edition revision. The first three are defined by USGS product standards, the fourth by an interagency
agreement with the U.S. Department of Agriculture Forest Service (FS). Numbers of each type of revision produced
from 1996 to 2000 are shown in figure 5.
Minor Revision. Revision candidate quadrangles are compared to recent aerial photographs to determine how much
change has occurred since the last map revision. If changes are small and few in number, the map may need only
minor revision. Names and boundaries are updated using information from local sources and other maps.
Corrections on file are made and the map collar is updated.
Basic Revision. Basic revision uses aerial photographs from the National Aerial Photography Program (NAPP) to
update a subset of map features. DOQ’s made from NAPP photographs are the primary data source. The DOQ's are
used for horizontal position control and for feature interpretation. Stereopairs of the same NAPP photographs aid
feature interpretation. In some cases, field checks may be performed by volunteers or by State cooperating agencies.
Name, boundary, and collar updates are similar to minor revision. Basic revisions may or may not include contour
updates.
Even though it depends almost entirely on remote sources, basic revision is not cheap. Basic revisions done with
USGS Government labor in 1998 and 1999 required an average of 280 hours per quadrangle, or approximately
$17,000. Although costs for contractor-produced revisions in 1999 were comparable, they are expected to decrease
as contractors gain experience with USGS standards.
Complete Revision. Complete
revision updates all standard
feature content, including
contours. Information is field
checked. This is very expensive
and is therefore rarely done. Only
four USGS quadrangles were
completely revised between 1995
and 2000. Complete revision of
these four was possible because a
State agency did the field
verification work.
Single Edition. In 1993, the
USGS and the FS signed an
interagency agreement to begin a
joint single-edition mapping
program. The content of the maps
includes features normally shown
on USGS maps, with additional
features required for the
management of National Forest
System land. Under the
agreement, 7.5-minute
quadrangles that contain National
Forest land are revised by the FS
but are printed and distributed by
the USGS. There are about
10,000 7.5-minute single-edition
map cells. Procedures for singleedition
updates are controlled by
the FS and are similar to USGS basic revision procedures. The interagency agreement allows the FS to update only
the National Forest land on a quadrangle and leave the other areas of the map unrevised. In these cases, the
0
200
400
600
800
1000
1200
1400
1600
1996 1997 1998 1999 2000 number of quadrangles
Basic
Minor
Forest Service Single Edition
Forest Service 32 1,271 696 630 400
Minor 83 340 356 255
Basic contour 5 26 27
Basic 311 145 106 129 210
Total 343 1,499 1,146 1,141 1,200
Figure 5. Numbers and types of recent revisions. Basic revision and
basic with contour revision are combined in the bar graph. The data show
the year that production work was finished; source photography dates
average about 3 years earlier.
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remainder of the map is part of the USGS revision pool. The two organizations have different requirements and
criteria for selecting maps for revision, so revision of forest and non-forest land is usually not concurrent.
Many of the blocks of newest maps in the western States shown in figure 4 are the result of single-edition revisions
in National Forests.
Revision Numbers and Effect on Series Currentness
The map revision program is driven by high sellers and cooperative funding. Map revision is not implemented as a
cyclic program that is guaranteed to keep all maps up to date.
Nevertheless, it is interesting to examine the
effect of different production scenarios on
series currentness. Figure 6 shows the results
of a simple simulation run against the "most
recent revision" dataset shown in figure 2. In
the simulation, a fixed number of the oldest
maps in the series were revised each year,
starting in 2000. The simulation assumed
2-year-old source materials.
Figure 6 illustrates that if the 1,500 oldest
maps are revised each year, the median age
of the series remains near its present value of
20 years. If fewer than 1,500 maps are
revised each year, the median age of the
series increases. If more than 1,500 maps are
revised each year, the age of the series
decreases. Both the increase and decrease
reach a limit that is a simple function of the
number of maps revised per year and the age
of the source materials.
Fewer than 1,500 maps are currently being
revised each year (fig. 5), and revisions are
not necessarily of the oldest maps.
Therefore, it is safe to assume that the
median age of the 7.5-minute map series is
increasing.
Figure 6 illustrates the extreme difficulty of
ever making the entire series "current." Even
if the present map revision rate was increased five-fold, the median age of the series would still stabilize at about 6
years with the age of the maps evenly distributed between 2 and 12 years.
DATA SOURCES
The current USGS revision program was not designed to do replacement mapping. Most revision work is done
using remote and secondary sources, including the original map, recent aerial photographs, information from other
maps, and information from other Government agencies. Following are the major sources of data.
Aerial Photographs and Digital Orthophotos
DOQ's are the most critical input to basic revision. They are made using horizontal control that is usually
independent of the topographic map, and the average USGS DOQ is positionally more accurate than the average
topographic quadrangle. An objective of basic revision is, therefore, to make the revised map match the DOQ.
0
5
10
15
20
25
30
2000 2005 2010 2015 2020
Currentness, years before present
1,000 maps/year
1,500 maps/year
2,000 maps/year
2,500 maps/year
5,400 maps/year
Figure 6. Improving currentness of the entire map series. A
simple simulation that shows the effects of revising a fixed
number of the oldest maps each year.
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Major planimetric features, especially roads and buildings, can be collected directly from a DOQ in computer-aided
drafting software systems.
DOQ's are made from NAPP photographs, and basic revision compilers also use stereopairs of the original
photographs to assist with feature interpretation. The current NAPP plan calls for full coverage of the continental
United States in 7 years (1997-2003). This schedule is subject to availability of funding, including State cooperative
funding (USGS, 1996).
DOQ’s made from the most recent photography do not always exist. The NAPP, the DOQ program, and the map
revision program are not closely coupled; each has its own customer base and its own funding sources.
Nonavailability of recent aerial photographs, a recent DOQ, or the control needed to make a DOQ can make it
impossible to revise a particular map.
The photographs for the original 7.5-minute program usually had scales of 1:15,000 to 1:25,000. The NAPP
photographs used for revision have an average scale of approximately 1:40,000. The smaller scale has some effects
on the accuracy of the revision, especially on contour updates.
Other Government Agencies
The USGS depends on other agencies for some types of data, particularly boundaries. When a map is authorized for
revision, requests for up-to-date boundary information are sent to Federal, State, and local government agencies.
The elapsed time between requesting and receiving these data can be a significant factor in the total time required to
revise a map.
State agencies participating in cooperative mapping projects may also elect to do field verification work to improve
the accuracy and completeness of the map content.
Geographic Names Information System
The Geographic Names Information System (GNIS) database is the official repository of feature names for the
United States. Names and feature locations are checked against the GNIS and changes are included on every
topographic map revision.
Earth Science Corps
The USGS has a volunteer program that allows private citizens to contribute to the earth science mission of the
agency. The Earth Science Corps is the field component of the volunteer program, and it includes an ongoing map
annotation project where volunteers collect new information to be used in the National Mapping Program. As of
October 1999, about 3,100 quadrangles had been assigned to 2,400 volunteers.
CONTOUR UPDATES
Elevation contour lines are the signature feature of USGS topographic maps. Much of the other information on a
7.5-minute map can be found on other types of maps, but until the recent development of airborne laser and radar
ranging technologies, there were no other sources of elevation data with comparable coverage and accuracy.
USGS map revision programs have always assumed that topography is much more stable than planimetry. A new
road or subdivision disturbs the land surface slightly, but rarely is the disturbance enough to warrant major revision
of contour lines with 10-, 20-, or 40-foot intervals. The current map revision program is explicitly tied to DOQ’s,
and contours cannot be revised from these monoscopic images.
Basic revision follows these guidelines for revising contours:
• Contours are revised only as part of joint funding agreements; that is, only when another agency is willing to
share the cost. Revising contours can increase the cost of a revision by 50 to 100 percent.
• The contour overlay is not completely recompiled but rather is updated in areas of significant topographic
change. The original map base is used for vertical control.
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• In areas of insignificant topographic change, "logical contouring" is used to preserve registration with other
features. For example, contours are squared across new roads and routed around new ponds without
stereorecompilation.
Contours are revised with NAPP stereophotographs, which are usually smaller scale than the photographs used to
compile the original contours. Therefore, improving the accuracy of existing contours is usually not possible except
in areas of very significant surface disturbance. This is consistent with the overall objectives of the revision
program, which are to maintain the horizontal and vertical accuracy of the existing map.
Most basic revisions do not include contour updates (fig. 5), which means that the topography and planimetry on the
revised graphic have different currentness dates. In some cases, this leads to glaring visual artifacts, such as contour
lines in large water bodies or new islands with no topography.
HORIZONTAL ACCURACY
The USGS originally compiled topographic maps using procedures designed to meet the National Map Accuracy
Standards (NMAS). Basic revision procedures were originally designed to retain the accuracy of the existing map
but not necessarily to improve it. This objective has shifted in the last 2 years, and now the horizontal accuracy
goals of basic revision are that the revised map should be at least as accurate as the previous version and that all
features should match the DOQ to within at least 73 feet. Both goals are evaluated by statistically comparing the
map to the DOQ.
The accuracy of old map bases can sometimes be improved by warping the base to fit newer control. When
appropriate, the USGS incorportates such methods into revision processes (Moore, 1999).
DISCUSSION
Table 1 shows the Congressional appropriations for the NMP in fiscal year 2000. In addition to these appropriated
funds, the total NMP budget included about $50 million from other agencies for jointly funded projects.
Table 2 summarizes production figures for
some of the more important NMP data
products in 1999, the most recent year for
which these figures are available. Data
production is funded partly by the Mapping
Data Collection budget line item (Table 1)
and partly by other Government agencies
through Joint Funding Agreements (JFA).
The exact dollar cost of the programs, as well
as the proportions funded through JFA’s,
have not been published. However, some
inferences about cost can be drawn from JFA
prices and other known data production
costs.
For example, it costs about $800 to make one
DOQ quarter-quadrangle (a 3.75-minute
cell), so the total 1999 DOQ production cost
about $48 million. Up to half of this may
have been paid by JFA partners.
The 1,141 topographic maps include 630 FS single edition revisions, 356 USGS minor revisions, and 155 USGS
basic revisions (fig. 5). Minor revisions cost about $1,100 and basic revisions about $17,000 per quadrangle. The
total cost of USGS map revision in 1999 was therefore about $3 million. As with DOQ’s, up to half of this cost
could have been paid by JFA partners.
Table 1: 2000 National Mapping Program
Budget
Mapping Data Collection 56.3
Information Management and Delivery 34.2
Geographic Research 36.1
National Mapping Program Total 126.7
From the USGS Fiscal Year 2001 Budget Justification. Figures
are in millions of dollars. These figures were compiled in mid-
2000 and are therefore estimates of final expenditures for FY
2000. The Information Management and Geographic Research
line items are not discussed in this paper.
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These data illustrate that images are more important to today’s NMP than topographic line maps. This is not
particularly surprising; images are not only cheaper than line maps, they are easier to keep current. Image products
therefore attract more cooperative funding, which is a major driver of NMP production decisions.
Traditional maps have two advantages over
images: they show features that cannot be
seen on images, and they present data with a
greatly enhanced signal-to-noise ratio --
selected features are interpreted by the map
producer and represented with clear symbols.
But both of these advantages are very
expensive. Correctly locating and classifying
features such as survey markers, cemetaries,
hiking trails, wells, and historical points of
interest requires field work. Drawing
contour lines, roads, and streams that are
both accurate and visually appealing requires
human craftsmanship (fig. 7).
It is possible that the traditional topographic
quadrangle is a product whose time has
passed. Perhaps these maps were appropriate
for the industrial age of the 19th and 20th
centuries, but not for the information age of
the 21st century. It may be that such maps
cannot be made fast enough to meet modern
users’ expectations of "currentness." It is, for
example, very difficult to imagine any combination of technical advances and budget conditions that would allow
the 7.5-minute map series to be made to their original standards and also allow a large percentage to be kept current
to within 5 years of the present.
On the other hand, this might be true only if we insist on retaining the artistic appearance and elegant data
integration of the traditional topographic quadrangle. Different products with comparable information content could
be maintained more easily. Such products include combinations of images (orthophotographs, satellite imagery),
gridded elevations, names from databases, and GIS vectors.
These types of image-based products, when compared to traditional topographic maps, would likely have these
characteristics:
Table 2: Selected Core Data Base Production, 1999
National Hydrologic Dataset
1:100,000-scale cataloging units
1,800
National Elevation Dataset
7.5-minute quadrangles
4,400
Digital Ortho Imagery (DOQ)
3.75-minute quadrangles ("quarter quads")
60,100
Topographic Map Series
7.5-minute quadrangles
1,141
Satellite Land Remote Sensing Data
Scenes processed
142,000
From the USGS Fiscal Year 2001 Budget Justification.
Numbers of production units are not directly comparable for
several reasons, including different product scales.
Figure 7. Topographic map artwork. The
image is a piece of a 7.5-minute topographic map
in south central Missouri. This fragment covers
about one quarter of one square mile, so
approximately 12 million pieces this size are
needed to cover the continental United States.
The spring, cabin, power line, and
four-wheel-drive road (single dashed line)
probably cannot be seen on an aerial photograph,
and so are on the map only because
photointerpretation was done in the field. All
linework was scribed by hand. Today linework
is drawn on a computer screen with drafting
software, but every new line must still be drawn
by a person.
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• Higher total information content, but less elegant presentation.
• More friendly to computer analysis, less friendly to human interpretation.
• More data overall because of the image base, but less consistency of content between maps because of
using "best available" data sources for map linework.
• Could be kept more current at lower cost.
The USGS is investigating several alternative graphic products as potential replacements for the 7.5-minute map
series. One proposal is to use a DOQ as a base, retain the 7.5-minute format with traditional collar and cartographic
grids, and overprint selected linework and names on the DOQ. Key to this concept is taking the map linework from
digital GIS databases created by other Government agencies, or even by commercial organizations. Using existing
data would increase speed, reduce costs, and allow the map to use the best and most current sources. However, it
also raises problems of data consistency and cartographic presentation. Few feature layers have been captured in
nationwide databases, so content would vary by State and region. The scale and positional accuracy of GIS
databases vary, so data from other sources may not register to each other or to the DOQ image base.
CONCLUSIONS
Up to 1,400 7.5-minute quadrangles per year are being revised. However, very few revisions include contour
updates, new control, or field verification of content.
Map revision standards and procedures currently in place will be used for at least several more years. The USGS
has no specific plans to return to a program of new 7.5-minute topographic mapping by collecting new control and
doing new field verification. In order to revise a greater number of maps with available funding, topographic map
revision will continue to be done with remote and secondary sources for the foreseeable future.
The USGS has active programs to improve the processes and lower the costs of topographic map revision. These
programs focus on integrating data from external sources, and therefore may lead to changes in map content and
symbol standards.
Traditional topographic maps are part scientific documents and part works of art. The artistic component -- shaping
contour lines to be visually appealing, for example -- is very expensive in both time and money, and perhaps is no
longer practical. Alternative products based on combinations of more modern data sources are being examined by
the USGS as potential replacements for the 7.5-minute topographic map series.
REFERENCES
Bohme, Rolf, 1989, Inventory of World Topographic Mapping. Published on behalf of the International
Cartographic Association by Elsevier Applied Science Publishers.
Moore, Larry; Harris, William; Kochis, Tim; Reed, Matthew, 1999, Raster Image Warping for Geometric Correction
of Cartographic Bases, URISA Conference Proceedings [August 1999 CD-ROM].
National Research Council, 1990, Spatial Data Needs: The Future of the National Mapping Program. National
Academy Press, Washington, D.C.
Schwartz, Seymour I. and Ehrenberg, Ralph E, 1980, The Mapping of America. New York, H.N. Abrams.
U.S. Geological Survey, 1996, The National Aerial Photography Program (NAPP). Reston, Virginia, U.S.
Geological Survey, 2 p. [fold out brochure].
U.S. Geological Survey, 2000. FY 2001 Budget Justifications and Annual Performance Plan. http://www.usgs.gov/
budget/2001_Justification/toctext.html. Printed copies available from the USGS Office of Budget and Organization
Analysis at 703-648-4430.