>> GIS Education
Thread views: 4463 View all threadsNext thread*Threaded Mode

(Stranger )
06/07/11 08:54 AM
Area calculations new Report this article as Inappropriate to us !!!Login to Reply

I've run into a strange quirk when calculating areas in different projections. My file is originally in UTM NAD83, but the client wants it converted to State Plane NAD83. When I do I get different areas for the polygons. In the UTM version I get 8000 acres, but in the State Plane version I get 8006 acres. We can't figure out what's going on. Any ideas?

(Stranger )
06/20/11 07:31 AM
Re: Area calculations new [re: sasnover]Report this article as Inappropriate to us !!!Login to Reply

If you're looking for exact areas, you need an equal area projection. 

But even then they won't agree.  This is because the software will assume a straight line in the current projection.  For sufficiently densified arcs they will agree.     

If you're working with ESRI products, I suppose the closest thing to exact would be Albers Equal Area (based on a cone), because it is the only one that is supported for an ellipsoid.  Lambert Azimuthal Equal Area (based on a plane), and Cylindrical Equal Area (based on a cylinder) are supported only for spheres.  There are some pseudoconic, pseudocylindrical, and pseudoplanar projections -- I think they are supported only for spheres.  There are some equations in one of Snyder's books for ellipsoids in LAEA but they've obviously been too hairy for ESRI to tackle. 




(Stranger )
06/20/11 08:31 AM
Re: Area calculations [re: maphound]Report this article as Inappropriate to us !!!Login to Reply

Thanks for responding! We're not exactly GIS novices at my company but we had never encountered this problem with area calcs before, probably because none of our clients have ever switched there preferred projection from UTM to Stateplane before. Unfortunately we are required to use the system our client wants, so we can't try out any of your suggestions on this project. Thanks for the info, though, very helpful.

View all threadsNext thread*Threaded Mode
Jump to


Textron - Countless CAD add-ons, plug-ins and more.

Internet Business Systems © 2016 Internet Business Systems, Inc.
595 Millich Dr., Suite 216, Campbell, CA 95008
+1 (408)-337-6870 — Contact Us, or visit our other sites:
AECCafe - Architectural Design and Engineering EDACafe - Electronic Design Automation TechJobsCafe - Technical Jobs and Resumes  MCADCafe - Mechanical Design and Engineering ShareCG - Share Computer Graphic (CG) Animation, 3D Art and 3D Models
  Privacy Policy