When working with spatial data you have to be very careful with matching the geographic coordinate systems and projections of your data. When a dataset is projected, 4 properties are affected and therefore you need to work with the right projections to minimize the distortion of the properties you are interested in studying. These 4 properties that are affected are:

1. Area
2. Shape
3. Distance
4. Direction

When working with new data you should carefully check the data before proceeding with any map creation or analysis. Here is a suggestion for a protocol you could follow to check and correct your data files.

1. Place all your shape files into one folder and open the folder in Arc Catalog.
2. Open the properties of each shape file (right click on the file -> properties) and check the coordinate systems, projections and datums are all present. Record this data so you can compare your multiple data files.
   • If any of this data is missing – check the description of the file to see if the coordinate system or projection it was originally created in is listed in the metadata (or check with the provider of the file for it), and assign the correct coordinate system or projection to the file by simply editing that field in the properties.
3. The next step is to review what projections your various data files are in and decide on the projection to use for your map (generally this should be based on what is commonly used in the field of study).
4. Now for the shape files that aren’t in the chosen projection, you can change the projecton using Arc Toolbox within ArcMap. Using the ‘Project’ tool, project each layer into the chosen coordinate system and projection.
5. Add the shape layers to your map and get to work!