Three units of measurement are commonly referenced when working within a map or scene: map units, location units, and display units.
Map units are the units in which the spatial data in the map or scene is drawn. Map units are determined by the linear coordinate system of the map or local scene.
Map units are read-only, and you can only change them by changing the coordinate system of the map or local scene. To do this, right-click a map or scene in the Contents pane and choose Properties from the context menu. The Map Properties dialog box appears. Click the Coordinate System tab, and choose a coordinate system from the list.
Location units are the coordinate units available to the project. These are listed on the Units tab of the Options dialog box. To add a unit, click <Select Unit Code>, and choose from the list of available units. To remove, format, or assign the default, right-click the unit. If you add a map or scene with a coordinate system in decimal degrees, and you previously set your default to linear units—such as feet or meters—the location units will revert to decimal degrees because the specified default is not applicable.
Display units are used by the coordinate system display at the bottom of the map or scene view. The values displayed are the real-world coordinate values corresponding with the pointer's location on the map or scene view.
To change the display units, right-click a map or scene in the Contents pane and choose Properties from the context menu. The Map Properties dialog box appears. Click the General tab, and choose a unit from the Display Units drop-down list. Alternatively, click the arrow beside the coordinates at the bottom of the map or scene view and choose a unit from the available list.