In the second half of the 20th century, the foundation of the U.S. Geological Survey’s national map series was the handcrafted 7.5-minute topographic map. Times change, budgets get squeezed and currency expectations become ever more challenging. The USGS's Larry Moore, who oversees data production operations at two National Geospatial Technical Operations Centers, provides an introduction to the new US Topo quadrangle maps.
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 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 Program
In 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 five 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 two 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 cost 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 high level of automation in US Topo production reduces cost and cycle times, but also contributes to lower visual quality. Current computer technology cannot reproduce the graceful appearance of a good hand-drawn map. Available software is especially weak at placing text, visually integrating different feature classes, and positioning crowded features while preserving clarity.
The Next Generation National Mapping Program
In the 1990s and early 2000s there was a consensus in the U.S. mapping community that the era of traditional quadrangle maps had ended. The belief was 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:
- 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.
- Modern coordinate systems with standard presentation. More than 95% 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% 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.
- 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 three-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.
- 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.
Figure 1. At about the halfway point of the original 7.5-minute mapping program (1970), maps had been published for 43% of the conterminous 48 states, and only 12% 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 three 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. Click for larger view.
The 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 have 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 three years, another important goal is continuous product improvement, including adding other feature classes to reach the content level of the old map series. The degree to which 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.
US Topo product information and download links here. US Topos are published in Portable Document Format (PDF), and can be downloaded free of charge.
More historical information on the original USGS topographic map series here.