# Points equally spaced in polygon, allowing for slope using ArcGIS Desktop?

I need to create a grid of points within a given area so that each point is 75m across the ground from any other point. The fish net tool would create the desired outcome on flat land but I need to take slope into account. I'm using this to allocate positions for a trap network for pest animal control and the site is relatively steep. I normally do this manually using contours and the buffer tool and just manually working out distance over ground for different slopes but I just wondered if anyone might know a better way?

I seek an ArcGIS 10.3 solution.

• Fishnet? I'd say you need triangular model made of 60 deg triangles. Perhaps gis.stackexchange.com/questions/185889/… Jun 11, 2017 at 9:45
• Please Edit the question to quantify "steep" and the reglarity of that steepness. Usually the vertical component doesn't add all that much, so that you could fudge the distance between a regular hexagonal tessellation. Unfortunately, that was a feature added at ArcGIS 10.4, but there are appropriate equivalents if you look for them. Jun 11, 2017 at 12:12
• If you need an answer in QGIS or Manifold as well or instead just ask it as a separate question.
– PolyGeo
Jun 11, 2017 at 12:24

I need to create a grid of points within a given area so that each point is 75m across the ground from any other point

There are cases where this may be impossible mathematically. For illustration purposes, if you are laying a fishnet on the curved 3D earth surface with neighboring points 100 km apart from each other (about 1 degree apart) and in alignment with the lat/long grid.

If such a regular fish-net (in terms of ground distance) exists, and if you count the number of squares at the same latitude, then there is going to be about 360 of those squares on the equator, while there is going to be about 1 square at the north/south pole (considering the length of the parallel lines in those regions).

What this means is that you have to shift the points around, and the result you get is not a regular fishnet anymore (at least not something like the rectangular fishnets you can create on a plane).

Practically, I think if you write an algorithm for this (or do it manually), you often will have to finesse point locations to satisfy the distance requirement. There is no guarantee that you can always find the next point satisfying the distance requirement or that such a regular fishnet on the curved surface exist.

• I've been struggling with this problem on a case quite similar and never could find a satisfying answer, but not knowing how to explain it. So glad to find out somebody has an explanation at last :) Jun 11, 2017 at 7:42