# About GIS Coordinate Systems

Coordinate systems typically used in Geographical Information Systems (GIS) are referred

to as GIS coordinate systems.

CAD coordinate systems such as UCS and WCS describe points relative to the object

being modeled, not relative to a location on the surface of the Earth. GIS coordinate

systems, on the other hand, describe locations on the surface of the earth. GIS coordinate

systems handle significantly larger scales than CAD coordinate systems and deal with

issues such as the curvature of the earth and terrain, which are insignificant to

CAD coordinate systems.

There are two types of GIS coordinates systems that are commonly used. They are geographic

coordinate systems and projected coordinate systems.

## Geographic Coordinate Systems

Geographic coordinate systems take into account the curvature of the earth and a location

is commonly specified in terms of longitude, latitude and elevation.

Because the earth is not perfectly round, no single geographic coordinate system

is able to accurately define all locations on the surface of the Earth. Consequently,

various organizations define local coordinate systems, where measurements are taken

locally from a local datum.

Local coordinate systems are considered more accurate because they align more closely

with the Earth’s surface in that locality, in comparison to an Earth-centric datum.

Often, more than one coordinate system may cover the location you are interested in.

As a general rule of thumb, the coordinate system with its datum closest to that location

is considered to be the most accurate.

## Projected Coordinate Systems

Projected Coordinate Systems use a mathematical transformation to convert geographic

coordinate systems into a flat 2D representation. They use linear measurements for

coordinates. As such they make it possible to transform GIS coordinates to CAD coordinates.

## Mapping CAD Coordinates to GIS Coordinates

When you assign geographic location information to a drawing file (GEOGRAPHICLOCATION

command), you also assign a projected coordinate system to the drawing.

Typically CAD drawings are unitless and are drawn at 1:1 scale. You are free to decide

the linear unit a drawing unit represents. GIS systems, on the other hand, allow the

coordinate system to decide the linear units. In order to map CAD coordinates to GIS

coordinates, the system needs to interpret CAD drawing units in terms of linear units.

The system uses the setting stored in the INSUNITS system variable as the default

linear measurement of a drawing unit. However, when you insert geographic location

information, you have the option of specifying a different linear measurement (for

a drawing unit).

sp popular **GIS** software, data projected in latitude/longitude is often represented as a '**Geographic Coordinate System**'. For example, data in latitude/longitude if the datum is the North American Datum of 1983 is denoted by 'GCS North American 1983'.geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth. A GCS is often incorrectly called a datum, but a datum is only one part of a GCS. … Longitude and latitude are angles measured from the earth's center to a point on the earth's surface.GIS coordinate systems. CAD coordinate systems such as UCS …geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth. A GCS is often incorrectly called a datum, …geographic coordinate system is a three-dimensional reference system that locates points on the … A point has two coordinate values: latitude and longitude.… There are two common types of **coordinate systems** used in **GIS**: ○. A global or spherical **coordinate system** such as latitude–longitude.coordinate reference **systems** exist. In each **coordinate system**, **geographic** locations or features are described mathematically using **coordinate** values.Geographic Coordinate System. Most GPS receivers come out of the box set to use latitude/longitude coordinates. And many GPS users never …Geographic coordinate systems (lat/long) are based on a spheroidal (either truly spherical or ellipsoidal) surface that approximates the surface of the earth. A datum …