I have a collection of historical scanned topographic maps from the 19th century that have already been georeferenced (NAD 1927). I'm uploading the maps as JPGs into ArcMap and would like to use the editing toolbar to create polygon features which I can then measure the area of. When I click "Start Editing" I receive a message that there are no editable layers.
How can I create polygon and line features so I can get measurements? Is my problem uploading as a JPG? Also, will the area measurements even be accurate in this sense? I would like area displayed in meters or feet squared, but will just drawing a polygon around a lake on the map provide a correct measurement (assuming I can get to the point where I can draw a polygon)? I'm relatively new to GIS and feel as if this should be as easy enough task but I am struggling a lot with it.