Projecting fishnet grid using ArcGIS Pro

Question

I want to make a 20 mile by 20 mile fishnet grid over the state of Nebraska, with the origin at either the far southwest corner (approx 11,583,008.75W 5,011,971.55N m) or the far NW corner (approx 11,583,491.14W 5,312,014.51N m). I don't think the fishnet tool is working properly the way I am using it, as the gridcells are too small (they are not actually 20 miles square).

I am starting with the Nebraska shapefile downloadable here: https://www.nebraskamap.gov/datasets/nebraska::nebraska-state-boundary/explore?location=41.450388%2C-99.634628%2C7.86

I am adding the NE shapefile to the basemap, and then creating the fishnet with a template extent defined by the NE shapefile, and an x and y cell resolution of 32186.88 meters (20 miles).

Nebraska has an area of 77421 square miles, so there should be approximately 77421/400 grid cells = 193 or so. Figure there's going to be 250 or so, since the fishnet creates a square grid, and Nebraska is not square at the corners. When I do this, I am getting 400 cells, which is way too many, and the cells are too small.

How do I fix this?

If you select the template extent of the above shapefile, the only parameters you need to fill out are cell size width and height, both of which are 32186.88 meters. But,here they are.

My parameters are: Output Feature Class: my_grid.shp

Fishnet Origin Coordinate: X = -11583186.7033 Y = 4865930.3002

Template Extent: west: -11583186.7033 south: 4865930.3002 east: -10609647.7366 north: 5312215.9049

Y-Axis Coordinate: X = -11583186.7033; Y = 4865940.3002

Opposite Corner of Extent; X = -10609647.7366: Y = 5312215.9049

Geometry Type: Poylgon

Answer 1

By default, the fishnet calculation will be done using the the same projection as the inputs you've provided, in other words Web Mercator, which is inappropriate for really any geoprocessing. In this case, if you run Add Geometry Attributes for Geodesic Area on the outputs of your Fishnet run, you'll see that the actual area of each fishnet cell is approximately 230 sq mi, with big variability between cells.

Whenever working with an ArcGIS tool, I recommend setting many/most environment variables explicitly, or you will often get results that aren't what you want. You can always check the environment variables that are respected by each tool on the documentation page:

https://pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/create-fishnet.htm

For this tool, the variables include:

The key environments to look at here include the Output Coordinate System and Extent. If you set the Output Coordinate System to an appropriate projection (e.g., the NAD 1983 Nebraska State Plane) and the extent to the extent of the input Nebraska polygon, you will get a fishnet result as you expect, in this case with 264 cells with an area of 400 sq mi each.

Edit:

The above steps work only if the Map Coordinate System has also been set to the desired output projection. The Fishnet parameters and environments must be set after the map's coordinate system had been set: