Amanda Henley
Working With Coordinate Systems In ArcGIS
October, 2007
Coordinate Systems Quick Reference
Sheet
In ArcMap, a Data Frame adopts the coordinate system of the first layer
added. All other layers are projected on the fly to match.
ArcMap cannot project a layer on the fly if the layer’s coordinate system is
undefined.
Commonly Used Projected Coordinate Systems:
National: Albers Equal Area Conic, Lambert Conformal Conic
State-level mapping: State Plane Coordinate System
oState Plane units can be in feet or meters, State agencies
typically use Meters
Sub-State level mapping:
oLocal Governments (County, City) typically use NC State Plane
U.S. Survey Feet
oSmaller Study Sites: use UTM
NC covered by zones 16, 17 and 18-west to east- see
graphic @ top of page
For a good description of many different projections, see:
http://erg.usgs.gov/isb/pubs/MapProjections/projections.html
Datums
It isn’t always obvious when two layers are in different datums.
GPS uses WGS84 – global datum, similar to NAD83
A datum transformation is required when projecting a layer into a coordinate
system that uses a different datum.
The only datum transformation that is performed by ArcMap on the fly is
NADCON (NAD27 < > NAD83). Even though the transformation is done on
the fly, you will still get the Geographic Coordinate Systems Warning. This
transformation will be performed ONLY if the layers have their coordinate
systems defined. This transformation shouldn’t be used if your data
covers Alaska and Canada.
Datum Transformations in ArcMap Version 9.1:
NAD 1927 to NAD 1983 or NAD 1983 to NAD 1927 (goes both ways)
-for areas in the 48 contiguous states
Name Code Area of Use
NAD_1927_To_NAD_1983_NADCON 1241 United States (contiguous
48 states)
WGS 1984 to NAD 1983 or NAD 1983 to WGS 1984 (goes both ways)
-for areas in the 48 contiguous states
Name Code Area of Use
NAD_1983_To_WGS_1984_5 1515 United States (USA)-
lower 48 states.
