Mobile Library

GIS

NOTES:

This quick cheat sheet may help a user properly overlay layers on a map in ArcGIS. NOTE: You still may need to further define or re-project layers, and certainly those with Geographic Coordinates, in order to perform certain sorts of analysis (e.g., proximity analysis, distance measurement).
In the last two columns when it says "Then, set data view's projection," once the layers are properly defined the data view's projection can be set to anything (doesn't have to match).

Layer opened first	Geographic Defined	Projected Defined	Geographic Undefined	Projected Undefined
	Sets Data View	Sets Data View	Discerns Long/Lat Coordinates, but Data View still undefined	"Unknown Units"
Subsequent layer
Geographic Defined	No overlay problems	No overlay problems	No overlay problems	1. Define Projection tool on undefined layer 2. Then, set data view's projection
Projected Defined	No overlay problems	No overlay problems	1. Define Projection tool on undefined layer 2. Then, set data view's projection	1. Define Projection tool on undefined layer 2. Then, set data view's projection
Geographic Undefined	No overlay problems Discerns Long/Lat Coordinates	No overlay problems Discerns Long/Lat Coordinates	No overlay problems Discerns Long/Lat Coordinates	1. Define Projection tool on one layer 2. Define Projection tool on other layer 3. Then, set data view's projection
Projected Undefined	Use Define Projection tool on undefined layers	Use Define Projection tool on undefined layers	1. Define Projection tool on one layer 2. Define Projection tool on other layer 3. Then, set data view's projection	Overlays only if layers are really both the same units (just undefined); otherwise, must define each layer, then set data view

Geographic Defined: Durham, NC, Tracts (polygons) from 2009 Census TIGER Shapefiles
Geographic Undefined: Durham, NC Roads and Railroads (lines) from ESRI Census 2000 files
Projected Defined: NCDOT primary roads (lines)
Projected Undefined: Same as above, with ".prj" file renamed to hide projection information