Introduction

Normally we look at the world from ground level and we don't see much of it. We can see the car and the garage, but not the entire house because the garage is in the way. From above, though, places look radically different. Looking at larger pieces of the world in this
way, we can see the relation of one point to another--the relation of the garage to the house, say, or of the house to the neighborhood. That's why we make maps.

A map is simply a picture of a place, usually from directly above, with distances, directions, and scale accurately depicted. The U.S. Geological Survey (USGS)--the Nation's premiere mapmaker--makes topographic maps to show contours of the land as well as many features.

Sometimes maps are scanned into a computer to digitize them. The maps can then be displayed on a computer screen. These digitized topographic maps are called digital raster graphics (DRG). The full potential of a DRG is best realized when it's combined with other digital map data, thereby providing additional visual detail for viewing, extracting, collecting, and revising map information.

A map, though, is selective. It leaves out certain features in order to emphasize others. For example, on a road map you can see roads--they're more or less permanent--but you can't see cars. There is, however, a way to see the cars, and a lot of other things that maps leave out. That way is with aerial photographs. They provide a view of exactly what an area looked like from above at one instant in time.

Hawaiian Islands

Maps, these days, are routinely revised using aerial photographs, and it is also possible to get aerial photographs in digital form. These digital photographs share with maps the accurate measurements of distance and direction and are known as digital orthophoto quadrangles (DOQ). A DOQ is not a substitute for a map. For most casual and recreational uses, in fact, aerial photographs are best used in conjunction with maps. But because of its map-like qualities, a DOQ can be used for any number of professional cartographic and land-management purposes.

Through USGS business and cooperative research and development partnerships, several Web sites serve as an access point for viewing and retrieving samples of USGS maps and images online.

The links below will take you to selected USGS Business and Cooperative Research and Development Agreement partner sites where you may view USGS maps and aerial photo images from your Web browser.

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Microsoft TerraServer
Resulting from cooperative research by the USGS and Microsoft Corporation, the TerraServer provides free online access to USGS digital aerial photographs, known as digital orthophoto quadrangles, and to digital topographic maps, known as digital raster graphics. To learn more about these products, visit the USGS Digital Backyard.

MapMart by IntraSearch, Inc.
Online ordering of Digital Mapping and Aerial Photography. Specializing in USGS products – DLGs, DEMs, DRGs, and DOQQs – as well as custom mapping.


Maptech MapServer by Maptech, Inc.
Maptech's MapServer provides a free way to view, print and e-mail topographic maps, orthographic maps, aero charts and nautical charts online. The Maptech MapServer gives users access to the largest online database of both NOAA digital charts and USGS maps available in the world.

TopoZone by Maps a la carte, Inc.
TopoZone provides an interactive interface which allows users to view a seamless topographic map and feature database of the
entire United States, based on digital raster graphics. The site is accessible to anyone with an industry standard Web browser at no charge.