[UW-GIS-L] Geographic Transformation for NAD 1983 --> Sphere Mercator?

[A. Cooke]

City of Seattle GIS data uses:
NAD83 Washington State Plane North Feet (NAD_1983_StatePlane_Washington_North_FIPS_4601_Feet)

Google Maps uses:
WGS84 Mercator projection (GCS_WGS_1984)

You want to use one of the NAD_1983_to_WGS_1984 geographic transformations.  Likely _5 will be the most accurate for the Seattle Area.

Transformation:                               Area of Use
NAD_1983_To_WGS_1984_1     North American Continent.  Most accurate at southern Latitudes.
NAD_1983_To_WGS_1984_2     Alaska - Aleutians
NAD_1983_To_WGS_1984_3     Hawai'i
NAD_1983_To_WGS_1984_4     United States - 48 contiguous states, but is superseded by _5. This transformation method should no longer be used.
NAD_1983_To_WGS_1984_5     United States - 48 contiguous states
NAD_1983_To_WGS_1984_6     Quebec
NAD_1983_To_WGS_1984_7     Saskatchewan
NAD_1983_To_WGS_1984_8     Alberta

For more information about these, see: http://support.esri.com/index.cfm?fa=knowledgebase.techarticles.articleShow&d=24159

-Andrew


From: uw-gis-l-bounces at mailman1.u.washington.edu [mailto:uw-gis-l-bounces at mailman1.u.washington.edu] On Behalf Of JEFFREY S. LINN
Sent: Thursday, March 05, 2009 8:49 AM
To: 'uw-gis-l at u.washington.edu'
Subject: [UW-GIS-L] Geographic Transformation for NAD 1983 --> Sphere Mercator?

I'm trying to convert a few feature classes from the City of Seattle standard projection into something that can be displayed in Google Maps. The ArcGIS project tool won't let me project the data without a proper geographic transformation, but I have no idea which one I should be using.

I'd imagine that some of you out there have done this before. I'd appreciate any advice you may have.

---------
Jeffrey Linn
GIS Manager
Capital and Space Planning Office
University of Washington
(206) 543-5433

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