If you find these tutorials useful and would like to link to them from your own pages,please contact the Drew Spatial Data Center Director, Dr. Catherine Riihimaki via email. You are invited to leave comments or ask questions in any of the Comment areas of each tutorial page. In order for multiple map layers to work properly together, they must all use the same Coordinate System. The following directions will walk you through the process of checking your Map Layers/Shapefiles to find out which Coordinate System they are using and how to change them if they are different. By changing the name of the Shapefile/Map Layer in the Projection process, you've created a new Map Layer/Shapefile with the desired Coordinate System. You will need to add this new Map Layer to your map and/or Geodatabase, and remove the old Map Layer that uses the incorrect Coordinate System. Source.