If all the vector data is in DD, set a projection in the view Properties.
Setting the projection properties of a view is important for analyzing data. The projection properties of a view are set by choosing Properties from the View menu. Since the projection properties are set once for an entire view document, projected and unprojected data can not be displayed together in the same view.
Unprojected Data If the data in a view are unprojected (geographic coordinates), the map units will be set to decimal degrees. You can set a projection on the view document using the View Properties dialog and the map units will be set to the native units of the chosen projection. The source data remains unprojected.
Setting map units back to decimal degrees or unknown will remove the view projection.
Projected Data If the data in a view are projected, the map units must be set to the native units of the data's projection.
Image data is not affected by the settings in the View Properties dialog, and instead, should be georeferenced to the data/view's coordinate system.
Distance units can be set once the map units are properly set.