Licensing information Summary Overwrites the coordinate system information map projection and datum stored with a dataset. This tool is intended for datasets that have an unknown or incorrect coordinate system defined.
Scale Map projections can be constructed to preserve at least one of these properties, though only in a limited way for most. Each projection preserves, compromises, or approximates basic metric properties in different ways.
The purpose of the map determines which projection should form the base for the map. Because many purposes exist for maps, a diversity of projections have been created to suit those purposes.
Another consideration in the configuration of a projection is its compatibility with data sets to be used on the map. Data sets are geographic information; their collection depends on the chosen datum model of the Earth. Different datums assign slightly different coordinates to the same location, so in large scale maps, such as those from national mapping systems, it is important to match the datum to the projection.
The slight differences in coordinate assignation between different datums is not a concern for world maps or other vast territories, where such differences get shrunk to imperceptibility.
Tissot's indicatrix Tissot's Indicatrices on the Mercator projection The classical way of showing the distortion inherent in a projection is to use Tissot's indicatrix.
Construction of a map projection[ edit ] The creation of a map projection involves two steps: Selection of a model for the shape of the Earth or planetary body usually choosing between a sphere or ellipsoid.
Because the Earth's actual shape is irregular, information is lost in this step. Transformation of geographic coordinates longitude and latitude to Cartesian x,y or polar plane coordinates.
In large-scale maps, Cartesian coordinates normally have a simple relation to eastings and northings defined as a grid superimposed on the projection. In small-scale maps, eastings and northings are not meaningful, and grids are not superimposed.
Some of the simplest map projections are literal projections, as obtained by placing a light source at some definite point relative to the globe and projecting its features onto a specified surface.
This is not the case for most projections, which are defined only in terms of mathematical formulae that have no direct geometric interpretation.
However, picturing the light source-globe model can be helpful in understanding the basic concept of a map projection Choosing a projection surface[ edit ] A Miller cylindrical projection maps the globe onto a cylinder.
A surface that can be unfolded or unrolled into a plane or sheet without stretching, tearing or shrinking is called a developable surface. The cylindercone and the plane are all developable surfaces. The sphere and ellipsoid do not have developable surfaces, so any projection of them onto a plane will have to distort the image.
To compare, one cannot flatten an orange peel without tearing and warping it. One way of describing a projection is first to project from the Earth's surface to a developable surface such as a cylinder or cone, and then to unroll the surface into a plane.
While the first step inevitably distorts some properties of the globe, the developable surface can then be unfolded without further distortion. Aspect of the projection[ edit ] This transverse Mercator projection is mathematically the same as a standard Mercator, but oriented around a different axis.
Once a choice is made between projecting onto a cylinder, cone, or plane, the aspect of the shape must be specified.a map projection in which quadrilaterals formed by meridians and parallels have an area on the map proportional to their area on the globe an equal-area projection map of the globe; oceans are distorted in order to minimize the distortion of the continents an equal-area map projection showing.
• The tires have short metal projections to improve traction on snow and ice. • next year's sales projections • First Bank officials, however, contend they will find other means to bolster earnings and maintain their projections.
This is the Plate Carree Projection of Canada. The Plate Carree Projection is a grid system. The equator is used as the standard parallel, the poles are represented by parallel lines at the top and bottom of the projection, and each grid cell is a perfect square.
The Peters projection map used a rectangular coordinate system that showed parallel lines of latitude and longitude. Skilled at marketing, Arno claimed that his map more fairly displayed third world countries than the "popular" Mercator projection map, which distorts and dramatically enlarges the size of Eurasian and North American countries.
Cartograms as map projections W. Tobler University of California Santa Barbara, USA Since the time of Ptolemy years ago the objective of map projections has been to produce maps of high metric fidelity, and this is still the prime objective today.
Thus the emphasis on direction. The map projection is the image of the globe projected onto the cylindrical surface, which is then unwrapped into a flat surface. When the cylinder aligns with the polar axis, parallels appear as horizontal lines and meridians as vertical lines.
map projection, transfer of the features of the surface of the earth or another spherical body onto a flat sheet of paper. Only a globe can represent accurately the shape, orientation, and relative area of the earth's surface features; any projection produces distortion with regard to some of these characteristics. Definition of Keywords in the Image Map Projection Group for ISIS. Certain keywords will always appear in the IMAGE_MAP_PROJECTION group in ISIS cube file labels if the cube is in a map projection. conic projection; conical projection (a map projection of the globe onto a cone with its point over one of the earth's poles) equal-area map projection ; equal-area projection (a map projection in which quadrilaterals formed by meridians and parallels have an area on the map proportional to their area on the globe).