Which Projected Coordinate System and datum is this data in?

State Plane Hawaii, Zone 3 (Oahu), Feet and NAD 83 Harn datum. Why Nad 83 Harn? It supports the use of survey grade GPS, it is more accurate than NAD 83 and has become the modern standard at the National Geodetic Survey. Efforts are underway to convert all our data to this projection at the City and all data on this public map service is Nad 83 Harn with the exception of the 1 Ft NGA Imagery. The full projection information is below:

Projection: State Plane Hawaii Zone 3 (Oahu) Coordinate System

ArcGIS Projection File Name: NAD_1983_HARN_StatePlane_Hawaii_3_FIPS_5103_Feet

Datum: NAD 83 Harn

Units: Feet

Spheroid: GRS 1980

What is NAD 83? From the NGS FAQ (http://www.ngs.noaa.gov/faq.shtml)

The North American Datum of 1983 (NAD 83) is "The horizontal control datum for the United States, Canada, Mexico, and Central America, based on a geocentric origin and the Geodetic Reference System 1980.

"This datum, designated as NAD 83, is the new geodetic reference system. ... NAD 83 is based on the adjustment of 250,000 points including 600 satellite Doppler stations which constrain the system to a geocentric origin." (Geodetic Glossary, pp 57)

What is HARN?

A High Accuracy Reference Network (HARN) and a High Precision Geodetic Network (HPGN) were two designations used for a statewide geodetic network upgrade. The generic acronym HARN is now used for both HARN and HPGN and was adopted to remove the confusion arising from the use of two acronyms. A HARN is a statewide or regional upgrade in accuracy of NAD 83 coordinates using Global Positioning System (GPS) observations. HARNs were observed to support the use of GPS by Federal, state, and local surveyors, geodesists, and many other applications. The cooperative network upgrading program began in Tennessee in 1986. The last field observations were completed in Indiana in September 1997 after horizontally upgrading some 16,000 survey stations to A-order or B-order status. Horizontal A-order stations have a relative accuracy of 5 mm +/- 1:10,000,000 relative to other A-order stations. Horizontal B-order stations have a relative accuracy of 8 mm +/- 1:1,000,000 relative to other A-order and B-order stations Of these 16,000 stations, NGS has committed to maintaining about 1,400 survey stations, named the Federal Base Network, and the various states will maintain the remainder.

ArcGIS Projection File Details:

PROJCS["NAD_1983_HARN_StatePlane_Hawaii_3_FIPS_5103_Feet",GEOGCS["GCS_North_American_1983_HARN",DATUM["D_North_American_1983_HARN",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",1640416.666666667],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-158.0],PARAMETER["Scale_Factor",0.99999],PARAMETER["Latitude_Of_Origin",21.16666666666667],UNIT["Foot_US",0.3048006096012192]]

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Data contained in these files or on this Web page is the property of theCity and County of Honolulu, Hawaii (City). The GIS data are proprietary to the City, and title to this information remains in the City. All applicable common law and statutory rights in the GIS data, including, but not limited to, rights in copyright, shall and will remain the property of the City. Information shown on these maps are derived from public records that are constantly undergoing change and do not replace a site survey, and is not warranted for content or accuracy. The City does not guarantee the positional or thematic accuracy of the GIS data. The GIS data or cartographic digital files are not a legal representation of any of the features in which it depicts, and disclaims any assumption of the legal status of which it represents. Any implied warranties, including warranties of merchantibility or fitness for a particular purpose, shall be expressly excluded.