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 …