How are different map projections used?
The method used to portray a part of the spherical Earth on a flat surface, whether a paper map or a computer screen, is called a map projection. No flat map can rival a globe in truly representing the surface of the entire Earth, so every flat map misrepresents the surface of the Earth in some way. A flat map can show one or more--but never all--of the following:
- True directions
- True distances
- True areas
- True shapes
Different projections have different uses. Some projections are used for navigation, while other projections show better representations of the true relative sizes of continents.
For example, the basic Mercator projection yields the only map on which a straight line drawn anywhere within its bounds shows a true direction, but distances and areas on Mercator projection maps are grossly distorted near the map's polar regions. On an equidistant map projection, distances are true only along particular lines, such as those radiating from a single point selected as the center of the projection. Shapes are more or less distorted on every equal-area map.
The scale of a map on any projection is often crucial to the map's usefulness for a given purpose. For example, the extreme distortion that is present at high latitudes on a small-scale Mercator map of the World disappears almost completely on a properly oriented Transverse Mercator map of a small area in the same high latitudes. A large-scale (1:24,000) 7.5-minute USGS topographic map based on the Transverse Mercator projection is nearly correct in every respect.
The USGS Map Projections poster summarizes and compares eighteen common map projections and their uses.
Related Content
How do I find, download, or order topographic maps?
What are the projection, horizontal and vertical datum, format, and distributed tile extent of 3D Elevation Program (3DEP) contours?
What are the projection, horizontal and vertical datum, and resolution for 3D Elevation Program (3DEP) standard DEMs?
What is the State Plane Coordinate System? Can GPS provide coordinates in these values?
How are UTM coordinates measured on USGS topographic maps?
USGS Topo Base Map Refreshed and Other Updates
The “USGS Topo Base Map” service named “USGS Topo” has been refreshed with new data and design changes. In addition, several of the “Data Availability”, or “Data Index” services have new cloud hosted URLs.
Mapping Public Lands in the United States
The Protected Areas Database of the United States (PAD-US) is the official inventory of public parks and other protected areas in all U.S. states and territories.
Finding Yourself Outdoors
Updated USGS digital topographic maps feature more trails and other recreation points of interest
Mapping- UTM Grid conterminous 48 United States
The Universal Transverse Mercator grid that covers the conterminous 48 United States comprises 10 zones—from Zone 10 on the west coast through Zone 19 in New England. In each zone,coordinates are measured north and east in meters.