How to define the number of meters per pixel

Discussion created by meganccdecker on Feb 18, 2014
Latest reply on Feb 20, 2014 by meganccdecker
I am creating a map and I need to tell ArcGIS that each pixel is 135 meters across so that I can take some measurements. To be more specific, I have an image taken by a spacecraft of another planet's terrain. I basically need to tell ArcGIS what the resolution of the image is. How do I do this? Thanks in advance!