I am working with a shapefile that I have not been able to project to the Mass State Plane NAD83 meters (i.e., EPSG:26986) SRS using ArcMap's "Project" tool. The "Project" tool reports that "no datum conversion" is available between the SRS of the shapefile and EPSG:26968.

Taking a look at the parameters of the shapefile's SRS using ArcMap, gives the following:

  • Projected Coordinate System: NAD_1983_StatePlane_Massachusetts_Mainland_FIPS_2001
  • Projection: Lambert_Conformal_Conic
  • False_Easting: 200000.00000000
  • False_Northing: 750000.00000000
  • Central_Meridian: -71.50000000
  • Standard_Parallel_1: 41.71666667
  • Standard_Parallel_2: 42.68333333
  • Latitude_Of_Origin: 41.00000000
  • Linear Unit: Meter
  • Geographic Coordinate System: GCS_GRS_1980
  • Datum: D_GRS_1980
  • Prime Meridian: Greenwich
  • Angular Unit: Degree

This looks weird. I've never seen an SRS that looks like this one. It seems as though the shapefile has two (different) notions of which datum its SRS is using: NAD_1983_StatePlane_Massachusetts_Mainland_FIPS_2001 (see first bold text, above), and D_GRS_1980 (second bold text, above.)

As-is this shapefile, or at least its geometry, is useless for my purposes. ArcMap cannot correctly overlay it (using on-the-fly projection) with other data I'm using, and thus none of the geoprocessing tools will work correctly with it (e.g., spatial join with another dataset.) When an attempt is made to overlay this data with other data in ArcMap (using its on-the-fly projection mechanism), the shapefile data is way off from "ground truth", usually by around 40 meters.

This suggests some kind of datum mismatch to me, but it appears to be one that ArcMap is not capable of reconciling.

How can I project this shapefile to some well-defined, well-known SRS?

EPSG:26986 would be ideal, but I will settle for any other SRS that allows the data to subsequently be projected to EPSG:26986.

I have tried to get a handle on the origin of this problematical shapefile, but haven't been able to turn up much. It dates back possibly as long as 10 years, and the person/people who created it may or may not be around/available to answer questions. My best understanding is that it is the result of importing some data in EPSG:26986 (specifically, the Massachusetts state Road Inventory) into a transportation demand modeling tool called TransCAD.

  • Welcome to GIS SE. As a new user, please take the Tour. The only way "on-the-fly projection" (or Reproject) can work is if the original data file has the correct projection. This is actually one of the most common questions in this exchange, but there isn't much that we can do if some source in the past is, in effect, lying to you (and ArcMap or any other GIS). Note that the PCS having both a Projection and a Datum is not in any way suspect (it is, in fact, required that projected systems have a root GCS and datum). An invalid datum transform is likely responsible, but difficult to fix. – Vince Sep 29 at 19:39
  • Can you make the shapefile available to other members of SE GIS? Perhaps Dropbox, etc? – Stu Smith Sep 29 at 20:00
  • Hi Vince, I understand that a PCS having both a Projection and a Datum is not suspect. What I think is suspect is that the PCS and GCS have different datums; I've never seen that before. – Ben Krepp Sep 30 at 14:00
  • The problematical shapefile has been uploaded to Dropbox, per Stu Smith's suggestion: dropbox.com/s/16sjc27808lc8sh/problem_shapefile.zip?dl=0 this is a clipped version of the entire dataset, but is sufficient to expose the problem. – Ben Krepp Sep 30 at 14:23

Problem solved: Although I've not be able to track down the person who imported this data into TransCAD, I was able to get in touch with the person who exported this data from TransCAD, and walked through the choices available in the TraansCAD export dialog with him. I suggested selecting "No datum transformation" under "choice of datum" (or however exactly the combo box in question was labeled.) The resulting shapefile lines up perfectly with the other datasets we're working with in this project.

Thanks to everyone who chimed in with suggestions and/or advice.

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Here's my suggestion (without knowing exactly where [pun intended] you got the shapefile from.)

Outside of ArcGIS Desktop

  1. Copy the shapefile and all related files to a new folder so we don't mess anything up
  2. Delete the prj file from that new folder so the Shapefile appears to have an unknown projection

Inside of ArcGIS Desktop

  1. Use the Toolbox to find the Define Projection command and open it

  2. Point the tool to your shapefile in the new folder

  3. Finish running the tool to apply your 'correct' Stateplane projection by finding it in the dropdown lists (I presume this is the one you want?)

NAD83 Mass Stateplane Meters

  1. Test out how the shapefile behaves after the redefining of the projection goes
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  • Just a comment that the tool does not define a new projection, it just applies a selected one to the shapefile. – JasonInVegas Sep 29 at 23:40
  • Hi Jason, Thanks for your suggestion. A similar idea occurred to me after logging off yesterday evening. I gave your suggestion a try, and sad to say it didn't fix the problem. I'll be posting the problematical shapefile to a Dropbox location so others can take a look at it - per Stu Smith's suggestion, above, in a moment. – Ben Krepp Sep 30 at 14:03

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