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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.