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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.

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    To add some clarification, you cannot create polygon and line features in ArcMap if you do not have a layer to add them to. They are vector features. Your .jpg is a raster layer, which is a different data type. This question and answers detail the differences between the two data types: What are Raster and Vector data in GIS and when to use? – Get Spatial Nov 5 '15 at 0:34
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This should help get you started with editing: ArcGIS 10: Editing & Creating Your Own Shapefiles

You can also measure areas and distances without creating polygons using the measurement tool in ArcMap

You can't edit a scanned map directly, you need to create a polygon shapefile that will hold the polygons you draw on top of your scanned map. The first link above will help you get a polygon shapefile created and start editing.

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