This is the home page for ``drawmap,'' a software package that lets you draw maps using raw data downloaded from the U.S. Geological Survey (USGS). Drawmap was originally developed for use with the Linux® operating system, but it should also work under most variants of the UNIX® operating system. There is currently no version of drawmap for the Windows® operating system. On this site, you can download the software in source form, and you can view some sample maps. The following modified excerpt from the manual page describes what drawmap is, and what it does:

The U.S. Geological Survey, and other sources, support sites on the Internet with many gigabytes of raw geographic data, mostly for the USA. Drawmap draws maps, using a subset of the available data. The relevant subset includes:

• 250K Digital Elevation Model (DEM) files --- Each file covers a block, one-degree square, with a 1201 by 1201 grid of elevations (in meters). The extra sample in each direction is due to overlap of the DEM files at their edges. (Files for Alaska use smaller grids, with only 401 or 601 samples in the east-west direction.) For Hawaii and the "lower 48," the one-degree square is covered by elevation samples spaced 3 seconds apart; and you will often hear these files called 3-arc-second files. In terms of distance along the ground, the sample spacing varies with latitude. It is generally less than 100 meters. (The "250K" means that the data were digitized from a map at the scale of 1:250,000.) Files of this type are currently available for free download from the USGS.

 
• 24K Digital Elevation Model (DEM) files (in the 'classic' format or the SDTS format) --- These files usually result from digitizing a "quad" map sheet. (Each 1-degree block of latitude and longitude, covered by a 250K DEM file, is further subdivided into an 8-by-8 grid to produce smaller blocks called quads.) The number of samples in each direction varies, from quad to quad, but there is roughly one sample per second of arc. These files differ from the 250K DEM files in that the samples are spaced a fixed number of meters apart rather than a fixed number of arc-seconds. Because each quad represents an area that is 7.5 minutes of latitude by 7.5 minutes of longitude, you will also hear these files called 7.5-minute DEMs. The USGS provides 24K DEM data for free download, in the new Spatial Data Transfer System (SDTS) format. Some files in the older format are available from other sources, and may be available for purchase from the USGS.

 
• 100K Digital Line Graph (DLG) files (in the 'optional' format or the SDTS format) --- These files come in collections, each of which covers a quarter of the one-degree square covered by a 250K DEM file. The files contain information that allows segmented linear and polygonal features to be drawn on maps, including boundary lines, hydrographic features (streams, lakes, and so on), transportation features (roads, rail lines, pipelines, and so on), public land survey data, and hypsographic lines (the familiar contour lines of a topographic map). The different general classes of data come in separate files. Files of this type are currently available for free download from the USGS, in either the 'optional' format or the SDTS format.

 
• 24K Digital Line Graph (DLG) files (in the 'optional' format or the SDTS format) --- Like the 24K DEM files, each of these files covers a single quad. Except for their inherently greater detail, these files are essentially the same as the 100K DLG files. As with the 24K DEM files, these files are freely available in SDTS format, but are harder to come by in the 'optional' format.

 
• GTOPO30 files --- GTOPO30 files are similar to 250K DEM files, but with samples spaced 30 arc-seconds apart, and with a quite different format. (For the purposes of this manual page, you can consider GTOPO30 files as just another variety of DEM files.) While these files have relatively low resolution, they have the virtue of providing full coverage for the entire planet. Furthermore, they are currently available for free download.

 
• Geographic Names Information System (GNIS) files --- These files are basically lists of place names, with the addition of latitude/longitude and other information. They are available for free download.


If a DEM or DLG file is one of the above types, and is from the USGS, there is a good chance that drawmap can use it. However, given the range of available files, this is not a certainty.

Using the data in the various files, drawmap can produce various kinds of customized maps, including shaded relief maps (with or without roads, streams, place names, and so on) and topographic maps (again, with or without additional features).

The only type of map projection currently supported is not technically a projection at all, but simply a grid of latitudes and longitudes. (The word "projection" is a mathematical term describing the "stretching" of the earth's roughly-spherical surface onto a flat map.) Over limited areas, this latitude/longitude grid approximates a family of projections called cylindrical projections. By default, the grid is square, in the sense that 1000 pixels in the latitude direction represent the same number of degrees as 1000 pixels in the longitude direction. You can make the grid non-square by playing with the "-x" and "-y" options.

The output is an image, in SUN rasterfile format, which can be viewed with your favorite image viewer, or converted to other forms for display or hard copy output.

At the time this manual page was updated (January, 2001), various DEM, DLG, and GNIS files were available for free download by following appropriate links from http://mapping.usgs.gov/. For DEM and DLG files, the site provides a convenient graphical interface that lets you locate desired files by clicking on a map. This can be far superior to trying to guess which of hundreds of files contains the data you want. The DEM, DLG, and GNIS files, and the GTOPO30 files too, were also available via FTP from edcftp.cr.usgs.gov, in the pub/data directory.

If you provide all three types of files (DEM, DLG, and GNIS) as input, then drawmap will first produce a shaded relief map (or, when -c or -C is specified, a contour map), and then overlay it with data from the DLG files (with the data from each DLG file, in succession, being overlaid on all previous data), and then overlay everything with place names from the GNIS file. If you omit the DEM data, then the shaded relief (or contouring) is replaced by a simple white background.

Source Code

Sample Maps

There are three basic kinds of maps. The first is a 3-dimensional rendering of the region, as it might look if viewed from high above. I produced these renderings by using drawmap to generate a ``height field'' for use with the ubiquitous ``povray'' ray-tracing package. Elevations on these maps are exaggerated to make the relief stand out more sharply; and the land surface was rendered with a somewhat shiny appearance to give the slopes some reflective highlights. The renderings contain some bodies of water, which I generated by a procedure requiring a lot of manual effort. Only a few of the largest water bodies are included.

The second kind of map is a shaded relief map, produced by the drawmap program alone. These maps simulate a 3-dimensional appearance by shading the topography as if it were lighted by a near-horizon sun.

The third map type is a hypsographic contour map, also produced by drawmap alone. This type of map is essentially the same as the shaded relief map, except that the relief is replaced by hypsographic contours. Only one map of this type is included, for the San Francisco Bay Area, in order to save on storage space.

You may note several imperfections in these maps. First of all, with the exception of the world map, the color scheme in the 3-dimensional renderings and in the shaded relief maps is not ``natural.'' This is because I chose the colors to make it easier to distinguish elevation levels, rather than to make the maps esthetically pleasing. I gave some attention to making the lowlands ``plant-colored'' and the uplands ``mountain-colored,'' but this was not the primary goal. Drawmap currently supports 4 different color maps, each designed with a different goal in mind. The world map uses a color map that is designed to look more natural than the color scheme used in the other maps. If you are familiar with the `C' programming language, and with RGB color coding, it is straightforward to modify drawmap to add your own color scheme.

The USGS data contain large numbers of place names, rivers, streams, lakes, roads, railroads, boundaries, and so on. Drawmap allows some control over which of these features will be included. For these sample maps, I decided to limit such information so that the relief isn't hidden. (Place names, in particular can obscure the map. There are often enough place names that, if they are all included, they pretty much totally hide the relief. In fact, they can even overlay one another, sometimes several layers deep. Also, in urban areas, the various roads and streets can form a network that leaves very little relief showing through.)

All of these maps are in JPEG format, at a 75% quality level. This quality level saves on storage space, but produces some degradation of the images compared to the originals. The defects are particularly noticeable in areas containing black text on a white background.

Drawmap sometimes has difficulty with water bodies; it can readily draw lines around the bodies, but can't always figure out how to fill the bodies with solid blue. (The reasons for this limitation are discussed in some detail in the drawmap source code.) In the case of most of the maps shown here, my solution to this problem was to not ask drawmap to try to fill in bodies of water. Once the maps were drawn, I used an image editor to fill the bodies in manually. This technique can be effective, but it is not an error-free process. Thus, you should expect some (hopefully small) deviations from reality in the wet parts of the maps.

As mentioned above, the projection used by drawmap stretches the curved surface of the earth to form a rectangular grid of latitudes and longitudes. The earth has a circumference of about 40,000 km, or 24,900 statute miles, or 21,600 nautical miles. (For simplicity, we ignore the fact that the earth isn't quite a perfect sphere.) Since longitude lines form great circles around the globe, and since we measure latitude by moving north or south along a line of longitude, the distance along the earth's surface represented by 1 degree of latitude is about 111 km (or 69 miles, or 60 nautical miles) everywhere on earth. However, the distance represented by 1 degree of longitude varies (depending on the latitude where the measurement is made) according to the formula 111 cos(latitude). Thus, at the equator, a 1-degree by 1-degree patch of territory is approximately a square, 111 km on a side. At the poles, a 1-degree by 1-degree patch is roughly a skinny triangle, 111 km tall. For the limited-area maps shown here, the distance represented by one degree of longitude varies from about 91 km, at the latitude of Albuquerque, to about 73 km, at the latitude of northern Montana. The world map, of course, spans the entire range of possibilities.

As you can see, determining the distance between objects on these maps is non-trivial. As a rule of thumb, I usually just assume that 1 degree of latitude or longitude is about 100 km, or 60 miles. This is only a crude approximation, but is easy to remember when making eyeball distance estimates.

If you want better distance measurements, there are mathematical techniques for determining the distance between two points, given their latitudes and longitudes. (These techniques aren't discussed in the drawmap package, but you can probably find them if you do some research.) From a low-tech standpoint, it is hard to beat the simplicity of the wrap-a-string-around-a-globe method.

For maps that cover a small enough area, one degree of longitude covers roughly the same distance at the top of the map as it does at the bottom. For such maps, drawmap options can be used to stretch the latitude direction, so that one centimeter (measured on the map surface) covers a walking distance (measured on the surface of the earth), that is roughly equal whether measured in the horizontal or vertical direction. (Except for areas near the equator, the stretching will make a 1-degree by 1-degree map tall and thin, instead of square, so that the map resembles the shape of its corresponding patch on the globe.) In such cases, it becomes straightforward to produce an approximate distance scale for the map. The maps shown here were generated so that a 1-degree square appears square on the map. Thus, earth-surface distances cannot be easily measured on the map surfaces.

Except for the world map, the raw USGS elevation data used in these maps contain only 1200 samples per degree of longitude or latitude. This means that the samples are pretty widely spaced. To visualize this, imagine one and a half American football fields, placed side by side. The four corners of such an area would represent roughly the spacing of the samples used to generate the maps. As you can see, a lot of interesting topography can hide in the region between samples, so don't expect small details to show up. (The raw data used in the world map contain only 120 samples per degree, allowing even more details to fall through the cracks.)

Bear in mind that these maps are for entertainment purposes only. I am not a professional cartographer, and I can't guarantee their accuracy. Don't depend on them for anything important.

Yellowstone National Park and environs.
In each of these maps, Yellowstone National Park occupies roughly the lower right quadrant, and lies mainly in Wyoming. The large lake is Yellowstone Lake, 136 square miles in extent. If you look closely, particularly at the 3-dimensional rendering, you can make out the outline of the caldera sculpted by the most recent of the gigantic volcanic eruptions that blasted the area in the distant past. The caldera is an irregular ellipse, about 47 miles (75 km) long and 28 miles (45 km) wide. The upper portion of Yellowstone Lake lies inside the southeast edge of the caldera, but the caldera is much larger than the lake. (The entire caldera has roughly 10 times the area of the entire lake.) In the northwest quadrant of the map lies Three Forks, Montana. Nearby, the Jefferson, Madison, and Gallatin rivers (from the west, south, and east) join to form the mighty Missouri (flowing north). Lewis and Clark named the three Missouri tributaries after the President, Secretary of State, and Treasury Secretary. About 30 miles southeast of Three Forks, is Bozeman, where the Museum of the Rockies has an interesting collection of fossils and cultural artifacts. There are many good hiking trails in this region.
click for larger image (91,955 bytes)	click for larger image (261,506 bytes)

North-Central Montana.
The western edge of the map area brushes up against the foothills of the Rocky Mountains. The maps thus illustrate a transition region between the mountainous spine of the continent, on the left, and the vast Great Plains, on the right. Within the map area are several of the mountain ranges that form outliers to the Rockies. In the upper left are the Sweetgrass Hills. During ice-age glaciation, these hills formed ``islands'' of land in a sea of ice. The Bear's Paw Mountains are just northeast of center, with the Little Rockies just to their east. To the east of Great Falls are the Highwood Mountains. At their extreme eastern edge is Square Butte, which was a landmark for Lewis and Clark, and is said to be visible for 100 miles. The Missouri River enters the map area at the lower left and flows just south of the Bear's Paw Mountains, on its way east. Geologists say that, in days of yore, the Missouri flowed north of the Bear's Paw, but ice-age glaciers moved it down to its current location. On their way up the Missouri, Lewis and Clark had to make a long portage around the Great Falls, near the present-day city of Great Falls. Part of this stretch of the Missouri has been designated the Upper Missouri National Wild and Scenic River, and can be viewed by taking a float trip. In Havre, a buffalo jump and a restored below-street-level town illustrate some of the colorful history of the area. Great Falls is home to the Lewis and Clark National Historic Trail Interpretive Center, and also to the C. M. Russell Museum, with a collection of western art.
click for larger image (37,834 bytes)	click for larger image (421,656 bytes)

San Francisco Bay Area and environs.
Sacramento, the California state capital, is in the northeast quadrant. The Napa wine country is just north of the bay area, in the vicinity of the large semi-rectangular lake (Lake Berryessa). You may be able to trace the path of the world-famous San Andreas fault, which goes up the middle of the San Francisco peninsula, dives into the Pacific just south of the city, passes just outside the mouth of the bay, and then cuts across Point Reyes and runs north up the coast. There are many, many attractions in the bay area. Personal favorites include watching the hang gliders negotiate the coastal cliffs at Fort Funston, and visiting Mount Tamalpais and Muir Woods, across the Golden Gate Bridge to the north.
click for larger image (75,316 bytes)	click for larger image (244,737 bytes)	click for larger image (204,504 bytes)

Albuquerque, New Mexico, and environs.
Albuquerque is just west of center, near the bottom of the map, in the valley of the Rio Grande. Just to the east, the Sandia Mountains are a prominent local landmark. There is a tram to the top of Sandia Peak, or you can hike the mountain trails. Some people jump to the mistaken conclusion that New Mexico is a stand-alone country, because of its name. It is, however, one of the 50 United States; and just to the east of the map area is the state capital, Santa Fe, with over 200 art galleries. The Albuquerque International Balloon Fiesta® is a popular event; and there are lots of other interesting things to see and do in the area.
click for larger image (47,987 bytes)	click for larger image (175,451 bytes)

The World, Planet Earth, Sol III, Terra, home of the puny Humans.
Earth is a nifty place, with lots of popular travel destinations. The Grand Canyon and the Himalayas are favorite destinations for sentient beings from relatively flat planets. Biologists from all over the galaxy have visited the Galapagos Islands, which serve as a self-contained laboratory for the study of giant-turtle biology. Immature sapients from the Zthaphagh sector enjoy buzzing the locals with saucer-shaped craft.
click for larger image (93,111 bytes)