Coordinate System

INTRODUCTION:
               Coordinate systems enable geographic datasets to use common locations for integration. A coordinate system is a reference system used to represent the locations of geographic features, imagery, and observations, such as Global Positioning System (GPS) locations, within a common geographic framework.

Each coordinate system is defined by the following:

Its measurement framework, which is either geographic (in which spherical coordinates are measured from the earth's center) or plan metric (in which the earth's coordinates are projected onto a two-dimensional planar surface) Units of measurement (typically feet or meters for projected coordinate systems or decimal degrees for latitude-longitude)

The definition of the map projection for projected coordinate systems:

“Other measurement system properties such as a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y-directions “

Several hundred geographic coordinate systems and a few thousand projected coordinate systems are available for use. In addition, you can define a custom coordinate system.

Types of coordinate systems: GDI uses three coordinate spaces: world, page, and device. World coordinates are the coordinates used to model a particular graphic world and are the coordinates you pass to methods in the .NET Framework. Page coordinates refer to the coordinate system used by a drawing surface, such as a form or control. Device coordinates are the coordinates used by the physical device being drawn on, such as a screen or sheet of paper. When you make the call my Graphics. Draw Line(my Pen, 0, 0, 160, 80), the points that you pass to the Draw Line method—(0, 0) and (160, 80)—are in the world coordinate space. Before GDI can draw the line on the screen, the coordinates pass through a sequence of transformations. One transformation, called the world transformation, converts world coordinates to page coordinates, and another transformation, called the page transformation, converts page coordinates to device coordinates.

The following are two common types of coordinate systems used in a geographic information system (GIS):

A global or spherical coordinate system such as latitude-longitude. These are often referred to as geographic coordinate systems. A projected coordinate system such as universal transverse Mercator (UTM), Albers Equal Area, or Robinson, all of which (along with numerous other map projection models) provide various mechanisms to project maps of the earth's spherical surface onto a two-dimensional Cartesian coordinate plane. Projected coordinate systems are referred to as map projections. Coordinate systems (both geographic and projected) provide a framework for defining real-world locations.