I was given a point shapefile that does not have coordinate system. So, I need to specify it. I was told that this have following reference system.

  1. Coord. Sys. – 17 South (UTM)
  2. Units – US Survey ft
  3. Datum – WGS 1984 (7P)
  4. Geoid model – GEOID12A (Conus)

I have never seen options for specifying Geoid model in ArcGIS, and also, I have not seen WGS 1984 (7P). Except this, I am familiar with other information. These two things are confusing me. Will I be fine if I just use WGS_1984_UTM_Zone_17S?

Can someone help me if this is fine. Please suggest.

  • I have also been to that page, but I could not figure out how to provide this information while defining coordinate system. I am using ArcMAP 10.4.1. The option I can choose is only WGS 1984 for the geographic coordinate system, and WGS 1984 UTM Zone 17S for the projected coordinate system. I have not worked with WGS (7P), and have not messed around any Geoid for projection. Any suggestions? – Sami khanal Sep 21 '17 at 16:59

You've got a real mish-mash of a coordinate reference system.

UTM zones are usually in meters, not US survey ft. Try using the WGS 1984 BLM 17N (ftUS) definition. I think someone misinterpreted 17S where S is the latitude band, rather than the North/South zone. If the data is in the US, and not South America, it won't be in the 17 South zone.

The 'S' latitude band is between 32°N and 40°N.

However, GEOID12A is for NAD83 (actually 2011 re-adjustment) and NAVD88, not WGS84.

So would probably use the NAD 1983 BLM 17N (FtUS) definition with NAVD88 (ht) (USFt) as the vertical coordinate system.

Disclosure: Esri Product Engineer

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