# Working with Coordinate Systems

Every spatial location in ProjectWise is associated with a two-dimensional, planar coordinate system in which x measures horizontal distance and y measures vertical distance. Each point on the plane is defined by an x,y coordinate.

You can use multiple coordinate systems in the same datasource. If you do, you must set one of them as the reference coordinate system. The reference coordinate system is used to compare objects that are in different coordinate systems. In that case, both objects will be re-projected into the reference coordinate system before being compared. The reference coordinate system must be chosen carefully so that all other coordinate systems have a valid transformation path to it.

The first coordinate system you add from the dictionary is automatically set as the reference coordinate system. If you add two or more coordinate systems from the dictionary, then you can set a different coordinate system to be the reference coordinate system.

ProjectWise delivers a dictionary (coordsys.dty) of existing coordinate systems. You can select to add coordinate systems from the delivered dictionary, or you can add coordinate systems from a custom dictionary. To add custom coordinate systems, you must first use Bentley Map to create a custom dictionary that includes your custom coordinate system(s), and then you must manually add the dictionary to ProjectWise.

You can also add a local coordinate system to the datasource. This type of coordinate system is designed for use in campuses where data is always stored in local coordinates. Multiple local coordinate systems can be used in the same datasource (for example: terminal 1, terminal 2). You can also use a mix of local coordinate systems and coordinate systems from dictionary in the same coordinate system.

When working with local coordinate systems, no re-projection to a geographical coordinate system is possible. When performing spatial searches, only the documents with the same local coordinate system as the background map used to perform the search will be part of the search results. For example, if the background map "Terminal1" is used to perform the spatial search, only the documents with a spatial location that uses the same coordinate system as this background map will be found by the search.

Each coordinate system displays the following attributes: