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Problem: Projection definitions for some SDC layers in 'usa\census' are incorrect

Description

The coordinate system definition for these layers does not match the ESRI .prj extension or format for WGS 1984. Therefore, these SDC layers cannot be projected to a different coordinate system (datum).

The coordinate system for the following SDC layers in the data_update_2008\usa\census folder is 'Lat Long WGS84', instead of 'GCS_WGS_1984'.

areacode.sdc
blkgrp.sdc
counties.sdc
dtl_cnty.sdc
dtl_cnty_ln.sdc
dtl_st.sdc
dtl_st_ln.sdc

The coordinate system for these layers is defined as

GEOGCS["Lat Long WGS84",
DATUM["D_WGS_1984",
SPHEROID["World Geodetic System of 1984",6378137,298.257222932867]],
PRIMEM["Greenwich",0],
UNIT["Degree",0.017453292519943295]]


This definition for WGS 1984 does not match the one used by ArcGIS Desktop. Because it does not match, no existing geographic (datum) transformations will work.

Cause

Since the coordinate system definition for these layers does not match the ESRI PRJ name or format for WGS 1984, these layers cannot be projected to a new coordinate system that uses a different geographic coordinate system (datum).

The coordinate system definition should read:

GEOGCS["GCS_WGS_1984",
DATUM["D_WGS_1984",
SPHEROID["WGS_1984",6378137.0,298.257223563]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]]

Note:
The well-known text (WKT) string has been formatted to make it easier to read.

Solution or Workaround

Using ArcCatalog, copy any required layers to a local hard drive.

In Windows Explorer, change permissions on the files or folder that contains the data to allow read-write access.

Use the Define Projection tool in ArcToolbox to define the projection as WGS 1984.prj. This projection file is located in Coordinate Systems > Geographic Coordinate Systems > World.