You can define a new
global coordinate system
based on your own data or use a predefined coordinate system as a basis for creating your own. You can begin by defining
a new datum or ellipsoid, or use existing elements in your coordinate system definition.
NoteIf you create a coordinate system by duplicating and then editing an existing system in the , you will see a dialog box with sets of options listed on the left. Click each one to see related options. If you choose
or on the tab, you will see a wizard. The wizard displays sets of options on different pages: click to see the next set of options. The options are roughly the same for all these situations, but the wizard has a few extra
options at the beginning.
Specify Starting Point
If you are using the wizard, specify whether to start by defining (or modifying) a coordinate system, or to first define or
edit an ellipsoid or a datum. If you are editing a duplicate of an existing coordinate system, you do not have this option.
- Start With A Coordinate System
Create a coordinate system from scratch or modify an existing one.
- Start With A Datum
Create a datum from scratch or modify an existing one. When you are finished, you can create an ellipsoid or move on to create
the coordinate system. See Create Datum dialog box
- Start With An Ellipsoid
Create an ellipsoid from scratch or modify an existing one. When you are finished, you can move on to create the coordinate
system. See Create Ellipsoid dialog box
Specify Coordinate System
On this page of the wizard, specify whether to create a coordinate system from scratch or to modify an existing one. If you
are editing a duplicate of an existing coordinate system, you do not have this option.
- Create A New Coordinate System
If you select this option, specify the . Choose from the following:
- : A coordinate system defined on a two-dimensional surface. Unlike a geographic coordinate system, a projected coordinate
system has constant lengths, angles, and areas across the two dimensions.This coordinate system type uses linear units, such
as meters and feet.
- : A coordinate system that uses a three-dimensional sphere to define locations on the earth. It includes an angular unit of
measure, a prime meridian, and a datum (based on an ellipsoid). This coordinate system type uses angular units, such as degrees,
radians, grads, and mils.
- : A non-earth (NERTH) coordinate system. No ellipsoid or datum is required.
- Create A New Coordinate System From An Existing Coordinate System
If you are using an existing coordinate system, specify the coordinate system that will be the basis of the new one.
Create/Modify Coordinate System
You must specify a code and description for the coordinate system. The remaining fields are pre-populated if you are basing
this coordinate system on an existing one. You can use the pre-populated values or specify new ones.
Specifies a unique code for the coordinate system.
Specifies a description of the coordinate system.
Enter the data source from which the values for this coordinate system were taken.
Select the units to use for this coordinate system.
Select the category (or categories) in which this coordinate system will appear. Click the category name in the left-hand
list and click to move it to the right-hand list. AutoCAD Map 3D displays the categories in the .
- Referenced To
Select one of the following:
Select a projection. If you did not specify an ellipsoid or datum, the only options available are and . , , and are not required for these projection types.
The projection you choose determines how many projection parameters you must enter and the units you can use. The exact fields
vary according to the projection you select. Any of the following types of parameters could be included:
- Standard Parallels
Specify the northern and southern standard parallels for this projection. Standard parallels are used in conic projections
to define the latitude lines where the scale is 1.0. For a Lambert Conformal Conic projection with one standard parallel,
the first standard parallel defines the origin of the y-coordinates. Central parallel defines the origin of the y-coordinates.
- Central Meridian
The origin of the x-coordinates.
- UTM Zone Number
The Univeral Transverse Mercator system divides the earth into a regular, non-overlapping grid of zones, each 8 by 6 degrees.
The Transverse Mercator projection is defined between 80 degrees south and 84 degrees north. Beyond these limits, the Universal
Polar Stereographic (UPS) projection applies. In addition to the zone identifier in the form of a number followed by a letter
(for example, 28G), each UTM zone has a false northing and a false easting, which are constant:
- False easting (all zones): 500,000 m
- False northing (all zones in the Northern Hemisphere): 0 m
- False northing (all zones in the Southern Hemisphere): 1,000,000 m
- Projection Origin
Specify the origin of rectangular coordinates for this map projection. Longitude of origin defines the origin of the x-coordinates.
For example, the longitude origin of a conic projection is the line of longitude that is straight and perfectly vertical.
This longitude value can be converted to an X-coordinate of zero, and is usually specified as the center of the map. The central
meridian and longitude of origin parameters are synonymous.
Latitude of origin defines the origin of the y-coordinates. This parameter may not be located at the center of the projection.
In particular, for conic projections, this is often the nearest round number that is south of the southernmost extent of the
region to map. In that instance, you do not need to set a false northing parameter to ensure that all y- coordinates are positive.
- False Origin
When the central meridian bisects the mapping region, half of the X coordinates are negative values. An offset called the
false origin can be added to all coordinates to make them positive. The X coordinate of this offset is called the false origin
easting. The Y coordinate of this offset is called the false origin northing. This parameter is optional.
- Scale Reduction
To produce the smallest possible distance between the projection surface and any point in the region you are mapping, you
must specify a scale reduction factor. This is particularly important when you are mapping large regions. This parameter is
Specify Common Parameters
In a few cases, these parameters will not appear.
Specify the paper scale for the coordinate system. For most GIS systems, this is 1 because virtual maps are not limited to
Specify the quadrants in which the x- and y-coordinates are positive (usually East and North).
- Useful Range
Specify the minimum and maximum latitude and longitude for which this coordinate system is considered valid.
- Minimum Non-Zero Coordinate Values
Enter the lowest x, y values found in the positive quadrants.
Review Coordinate System
If you are using the wizard, review your settings. To change any of them, click next to that group of settings. When the settings are correct, click .