US Topo - A New National Map SeriesThis article was originally published in Directions Magazine http://www.directionsmag.com/articles/us-topo-a-new-national-map-series/178707
May 16, 2011
Reprinted with Permission, Copyright 2011 Directions Media.
Access readers who are not entirely familiar with some of the specialized mapping terms mentioned in this article are invited to see the Glossary following this piece.
In the second half of the 20th century, the foundation of the U.S. Geological Survey's (USGS) national map series was 7.5-minute topographic maps. This map series was declared complete in 1992. In the 1990s and early 2000s the USGS mapping program focused its attention on digital data for geographic information systems (GIS). In late 2008, the USGS began defining a new general purpose, digital, quadrangle map series named US Topo. Although this series is deliberately modeled on the older 7.5-minute printed quadrangles, it is different in important ways. Some of these differences are aesthetic and therefore visually obvious. A common user reaction is that the new maps aren't as good as the old printed topographic maps.
The original USGS topographic maps were handcrafted products created from primary data sources. US Topo maps are mass-produced from secondary data sources. While similar in some ways to the old maps, US Topo maps are a different product for a different time, and offer some important advantages over the older product.
The Original Topographic Mapping ProgramIn the original 7.5-minute topographic mapping program (circa 1945-1992), the USGS contracted aerial photography and sent government employees to the field to survey the map area. Field crews established horizontal and vertical control, located and classified cultural features, located permanent survey markers, hiked wilderness trails, classified natural features such as streams and swamps, collected boundary information from state and local governments, and investigated geographic names by interviewing local residents. This field intelligence, including heavily annotated aerial photographs, was returned to the regional mapping centers and compiled into standard maps. Control was added using aerotriangulation, contours were manually compiled from stereo aerial photography, almost all text was placed by hand, almost all lines were drawn by hand, and manuscripts would typically go through at least four edit cycles before being approved for publication.
Except for the use of aerial photography, this is basically how maps had been made since the mid-1700s. Quality maps were necessarily expensive due to this accepted practice. The cost of the 7.5-minute map series for the 48 conterminous states is estimated at about $3 billion, more than $50,000 per map (in 2007 dollars). The elapsed time from project planning to map printing was about 5 years, and it took more than 45 years to complete the series. At its peak in the 1960s and 1970s, the National Mapping Program employed more than 2,000 people. It is unlikely Congress would fund such a program today, or that today's map users would consider these cycle times acceptable.
The US Topo Program
US Topo quadrangle maps are mass-produced using automated and semiautomated processes. The cartographic content comes from national GIS databases. In the two years from June 2009 to May 2011, the USGS produced nearly 40,000 maps, more than 80 maps per work day. Only about 2 hours of interactive work are spent on each map, mostly on text placement and final inspection. The USGS has not yet settled on a model for calculating the costs of US Topos, but they are probably cheaper than the original topographic maps by at least a factor of 100.
The feature content of a US Topo depends directly on the source GIS databases. This creates problems for map completeness and quality:
- These databases were not designed for producing general purpose maps. Regardless of the accuracy of individual databases, data from different sources have different resolutions and collection dates, and visual integration between feature classes is usually a very low priority for the data owners.
- Many features traditionally captured by direct field observation are not in any public domain national database. Examples include minor features such as windmills, water tanks, fence lines, local parks, and recreational trails, but also more important features such as boundaries, pipelines, and power transmission lines.
- Using data gathered by other programs or organizations, instead of owning all phases of data gathering and map production, means responsibility for data quality is widely distributed, including organizations that are not stakeholders in USGS maps.
The Next Generation National Mapping ProgramIn the 1990s and early 2000s there was a consensus in the U.S. mapping community that the era of traditional quadrangle maps had ended. It was believed that GIS data would drive dynamic map systems, and so the USGS mapping program turned its attention to the design and construction of GIS databases. Though successful in many ways, these efforts did not lead to replacing the national map series. Building software systems to produce quality custom maps is more technically difficult than anticipated. GIS databases tend to be constructed for other purposes, with data models that are not necessarily friendly to map production. For some applications - including wildfire suppression, disaster response, homeland security, military operations, search and rescue, and recreational backpacking - GIS technology has not yet proved to be an adequate substitute for traditional maps.
US Topo represents a new type of national map series. The layout of the original 7.5-minute map series is iconic, and US Topo was deliberately modeled on the older maps in the belief that users would be comfortable with this design. Nevertheless, this similarity is superficial. It is no longer reasonable to create a national map series from primary sources, field inspection, manual data integration, and manual drafting. The US Topo program is a test of the hypothesis that a standard, general purpose map series relevant to the early 21st century can be created and maintained by other means.
The Meaning of Quality
It is clear to most map users that the old topographic maps have higher visual quality than US Topo maps. The old maps show more features, have better text design and placement, better visual integration, and a more graceful overall appearance. A traditional hand-drawn map is a marvel of data presentation, facilitating human processing of large amounts of information quickly and accurately. US Topo maps, although superior in this regard to a typical GIS display or plot, fall short of traditional map presentation standards.
On the other hand, there are at least four important ways in which US Topo maps are superior to the old map series:
1. The inclusion of a high-resolution orthophoto image. The technology and data for this did not exist during the original 7.5-minute mapping program. Even today, the US Topo is a unique source for a public domain image tile this large and conveniently packaged.
2. Modern coordinate systems with standard presentation. More than 95 percent of the older, printed maps are cast on the antiquated North American Datum of 1927 (NAD 27). None conform to the recently defined U.S. National Grid (USNG) standard, and only about 25 percent have Universal Transverse Mercator (UTM) grid lines. Casual map users may not be aware of these shortcomings, but they present serious problems for military, emergency response, and other professional uses.
3. Map currency. The original USGS topographic program took decades to cover the conterminous 48 states, so at any given time large areas of the country either had no coverage or outdated coverage (figure 1). The primary strategic objective of US Topo is to refresh the map series for the 48 conterminous states on a 3-year cycle. At a minimum, this cycle will provide current aerial photography in quadrangle format, and will allow other updated data to be published without delay.
4. A digital product, freely downloadable. Digital files with features organized in layers allow more data to be included, and also allow customized viewing and printing by users. Free distribution over the Web reduces time and expense for map users.
ConclusionsThe decision to revive the USGS quadrangle mapping program was made in November 2008. Production of relatively simple image maps began in June 2009. Contour and hydrography layers were added in October 2009. By May 2011 about 40,000 maps had been published.
The speed of this ramp-up is impressive. The rush to production and distribution of US Topos reflects the USGS commitment to a modern national map series, and a belief that making an up-to-date standard map widely available cannot wait for complete consensus on design or total availability of data.
Whereas the top priority of the program is to cover the conterminous United States in 3 years, another important goal is continuous product improvement, including adding other feature classes to reach the content level of the old map series. To what degree this goal can be achieved, and how quickly, remains to be seen. However, even the basic US Topo maps published in 2009 and 2010 justify the low cost of the program.
Update, September 2011
Over 50,000 maps will be published by the end of FY11, and about 54,000 by the end of calendar year 2011. This demonstrates the ability to refresh CONUS on a 3-year cycle, but will not actually gain full CONUS coverage due to National Forest areas that were skipped in 2009. Full coverage of CONUS will be achieved by the end of FY12, as well as replacing all 2009 "Digital Map - Beta" maps with US Topo contour maps. Map production over non-CONUS areas will also begin in FY12.
For US Topo product information and download links, see http://nationalmap.gov/ustopo/. US Topos are published in Portable Document Format (PDF), and can be downloaded free of charge.
For more historical information on the original USGS topographic map series, see http://topomaps.usgs.gov/
At about the halfway point of the original 7.5-minute mapping program (1970), maps had been published for 43 percent of the conterminous 48 states, and only 12 percent of the country had coverage that was current to within 10 years. Incomplete and out of date coverage is the hidden cost of traditional mapping technologies. A goal of the US Topo program is to map the entire country on a 3-year cycle. Both the old and new programs include Alaska, Hawaii, Puerto Rico, and U.S. territories; these areas introduce additional complexity, and are not discussed in this paper.
GlossaryAerotriangulation - (1) The determination of horizontal and/or vertical coordinates of points on the ground, from measurements of angles, distances, or coordinates of points on overlapping aerial photographs, and from already-known coordinates of points on the ground. Phototriangulation using aerial photographs. Although the basic principles had been established as early as 1759, real progress was not made until, in the early 1900's and particularly in the 1920's, the airplane became a practical carrier for the camera.(2) The theory and procedures used for determining such coordinates.
CONUS - The conterminous United States (the 48 U.S. states that are south of Canada and north of Mexico, plus the District of Columbia).
North American Datum of 1927 (NAD 1927) - The primary local horizontal geodetic datum and geographic coordinate system used to map the United States during the middle part of the twentieth century. NAD 1927 is referenced to the Clarke spheroid of 1866 and an origin point at Meades Ranch, Kansas. Features on USGS topographic maps, including the corners of 7.5-minute quadrangle maps, are referenced to NAD 27. Although NAD 83 became the official datum of the United States in the late 1980s, many maps cast on NAD 27 remain in use today Source: support.esri.com/en/knowledgebase/Gisdictionary/browse
North American Datum of 1983 (NAD 1983) - A geocentric datum and graphic coordinate system based on the Geodetic Reference System 1980 ellipsoid (GRS80). Mainly used in North America, its measurements are obtained from both terrestrial and satellite data. Source: support.esri.com/en/knowledgebase/Gisdictionary/browse
Orthophotograph - A photograph prepared from a perspective photograph by removing those displacements of points caused by tilt, relief, and central projection (perspective). Sometimes called an orthophotomap.
7.5-minute Topographic Map - The U.S. Geological Survey 1:24,000- scale topographic maps are commonly known as 7.5-minute quadrangle maps because each map covers a four-sided area (quadrangle) of 7.5 minutes of latitude and 7.5 minutes of longitude.
Topographic Map - There are maps of various kinds - road maps, political maps, land use maps, maps of the world - and each of these serves different purposes. A topographic map is distinguished from other types of maps by portraying elevation. Modern maps use contour lines to portray the shape and elevation of the land. Topographic maps render the three-dimensional ups and downs of the terrain on a two-dimensional surface.
Universal Transverse Mercator (UTM) grid - The UTM is a military grid system based on the transverse Mercator projection and applied to maps of the Earth's surface. This projected coordinate system divides the world into 60 north and south zones, 6 degrees wide. Polar regions are excluded in this projection. In 1978, the USGS implemented the use of the UTM grid on all published maps at the scale of 1:1,000,000 or larger. This grid did not replace previously used referenced systems, but was an addition to the map. The UTM system provides coordinates on a worldwide flat grid for easy computation.
U.S. National Grid (USNG) - A nonproprietary alphanumeric referencing system (GIS) for latitude and longitude. The USNG standard established a nationally consistent grid reference system, just as all street maps use a common set of street names. USNG provides a seamless plane coordinate system across jurisdictional boundaries and map scales; referencing with GPS, Web map portals, and hardcopy maps. Source: The Federal Geographic Data Committee.