The Albers equal area conic is the typical projection for historical USGS maps of the lower 48, it being a general-purpose low-distortion compromise for mid-latitude short and wide extents.
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Certain map projections, or ways of displaying the Earth in the most accurate ways by scale, are more well-known and used than other kinds. Three of these common types of map projections are cylindrical, conic, and azimuthal.
What map projections do we use?
| Projection | Type |
|---|
| Mercator | cylindrical |
| Robinson | pseudo-cylindrical |
| Transverse Mercator | cylindrical |
One of the most famous map projections is the Mercator, created by a Flemish cartographer and geographer, Geradus Mercator in 1569. It became the standard map projection for nautical purposes because of its ability to represent lines of constant true direction.
AuthaGraph. This is hands-down the most accurate map projection in existence. In fact, AuthaGraph World Map is so proportionally perfect, it magically folds it into a three-dimensional globe. Japanese architect Hajime Narukawa invented this projection in 1999 by equally dividing a spherical surface into 96 triangles.
World Geodetic System 1984
Geographic coordinate systems are based on a spheroid and utilize angular units (degrees). Projected coordinate systems are based on a plane (the spheroid projected onto a 2D surface) and utilize linear units (feet, meters, etc.).
Geographic information system
The two horizontal datums used almost exclusively in North America are NAD 1927 and NAD 1983.
Because SPCS needs such a high level of accuracy, it divides the United States into 124 zones, each with a projection of its own. Overall, the State Plane Coordinate System minimizes distortion (compared to the UTM system) because of the smaller zone sizes.
Projection basics the GIS professional needs to know. Coordinate systems , also known as map projections , are arbitrary designations for spatial data. Their purpose is to provide a common basis for communication about a particular place or area on the earth's surface.
The following are some reasons for using a projected coordinate system: You want to make accurate measurements from your map and be sure that the spatial analysis options you use in ArcMap calculate distance correctly.
The UTM system consists of 60 zones, each 6-degrees of longitude in width. The zones are numbered 1-60, beginning at 180-degrees longitude and increasing to the east.
The good news is that map projections allow us to distort systematically; we know exactly how things are being stretched or squashed at any given point. We have many different map projections because each has different patterns of distortion—there is more than one way to flatten an orange peel.
Explanation: The major difference in the map projections based on the area they distort as all he map projection are projected to some sort of the earth surface areas as they tend to depict the landmass in different areas as related to the shape, size and the direction of the projection of the landmass.
Often, the map projection is predetermined. If it is not predetermined, a lot depends on the map size, the scale, shape and location of the region of interest on the globe. Depending on the purpose, equivalent, conformal and compromising projections are used.
We can't have just one map projection because there is non-single map that creates a perfect image of the Surface of the Earth. That is why cartographers need various maps to overcome the problem of distortion. It could be areas distortion or distances distortions.
There are projections that make a good compromise of all three aspects. For mapping the whole US or North America in general Albers Equal Area Conic or Lamberts Conformal Conic are a good choice for most applications.
The mathematical equations used to project latitude and longitude coordinates to plane coordinates are called map projections. Inverse projection formulae transform plane coordinates to geographic.
A map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion. The mapmaker must select the one best suited to the needs, reducing distortion of the most important features.
Top 10 World Map Projections
- Mercator. This projection was developed by Gerardus Mercator back in 1569 for navigational purposes.
- Robinson. This map is known as a 'compromise', it shows neither the shape or land mass of countries correct.
- Dymaxion Map.
- Gall-Peters.
- Sinu-Mollweide.
- Goode's Homolosine.
- AuthaGraph.
- Hobo-Dyer.
Explanation: Orthographic projection is the representation of two or more views on the mutual perpendicular projection planes. But for oblique projection, the object is viewed in only one view.
The Gnomonic projection is geometrically projected onto a plane, and the point of projection is at the centerofthe earth. It is impossible to show a full hemisphere with one Gnomonic map.
The azimuthal equidistant projection is an azimuthal map projection. It has the useful properties that all points on the map are at proportionally correct distances from the center point, and that all points on the map are at the correct azimuth (direction) from the center point.
In addition, Mercator only distorts longitudinal distances (except very close to the poles), whereas Peters screws up the scale almost everywhere for both longitude and latitude. This is why Mercator beats out Peters in the world of cartography, and why Google Maps uses a modified Mercator projection.
The Robinson projection is unique. Its primary purpose is to create visually appealing maps of the entire world. It is a compromise projection; it does not eliminate any type of distortion, but it keeps the levels of all types of distortion relatively low over most of the map.
Projections are a mathematical transformation that take spherical coordinates (latitude and longitude) and transform them to an XY (planar) coordinate system. This enables you to create a map that accurately shows distances, areas, or directions.
