Creating fishnet where each point from point file is located in middle of individual grid cells?

Question

I have a point dataset in ArcGIS 10, and wish to create a fishnet, where each point is in the centre of an individual grid cell. Thus each point must be in the centre of a square.

I have used the Create Fishnet Tool, creating a fishnet with a cell size equivalent to the distance between my points. Then I have defined the projection of my fishnet to be the same as my point dataset.

My problem is that my points are located in the corners of the grid cells instead of in the centre. Is there any way of fixing this?

Answer 1

I can see two ways to do this.

1. After following your steps, you can edit the fishnet Feature Class. After Start Editing select all features from the fishnet and Move (Editor toolbar, dropdown menu) them. For X and Y you should set the half of cell size. The numbers should be positive or negative depending on the direction you have to move the grid.

2. While creating the fishnet you should use the point FC as Template extent. This way the left, top, right, bottom fields fill up. You should lower the left and bottom values with half cell size and raise the right and top values with half the cell size.

Answer 2

Calculate the min/max values for X/Y using the field calculator or similar for respective new fields:

• XMin
• XMax
• YMin
• YMax

Using a these functions:

!shape.Extent.Xmin!
!shape.Extent.Xmax!
!shape.Extent.Ymin!
!shape.Extent.Ymax!

Then calculate the centerpoint using:

• Xcenter = ((XMin + XMax) / 2)
• Ycenter = ((YMin + YMax) / 2)

The best would of course be to combine the above into one Python function whcih delivers the relevant coordinates or have it create a new spatial file.