I have two digital terrain models in ESRI ASCII (.asc) format. Their elevations intersect in multiple places. How can I extract the intersection of these two DTMs as a polyline or polygon shapefile?

Example: I'm after the dotted line in this figure as a polyline. enter image description here

2 Answers 2


This seems like more appropriate to solve with TINs, by the nature of the planes they create.

If you have access to the 3D Analyst extension in ArcGIS, I would follow these how to documents:

  1. Creating a TIN surface from raster data

  2. How To: Determine the plane of intersection between two TIN or terrain surfaces


Reclassify both DTMs and give them a value of 1. Then add the two reclassified DTMs together. Then convert the resulting summation to polygons. The polygons with an attribute of 2 represents the intersection.

  • 1
    Apologies but I think you've misunderstood my question. I'm not after the areas that the DTM coverage overlaps, but the locations at which the two DTMs cut into each other - the locations at which the two DTMs are equal. Jun 14, 2017 at 11:38
  • Use the Equal To tool in the Spatial Analyst Tools. Then convert the result to polygons.
    – GBG
    Jun 14, 2017 at 15:19
  • 1
    Hi GBG - thanks! We're a step closer. But there aren't necessarily equal values in the two DTMs. They contain elevations saved to 4dp that will cross over at multiple locations. I'm after a polyline of the dotted line in this example: i.stack.imgur.com/2gxWP.png Jun 15, 2017 at 7:26
  • I don't understand what 4dp means. Can you explain?
    – GBG
    Jun 16, 2017 at 15:35
  • Sorry - four decimal places. Jun 21, 2017 at 10:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.