Discrepancy between measure tool and expected distance of reference grid/fishnet

[EileenB]

Hi there,

I'm trying to create a grid of points spaced 400 m apart. I have tried to use the Create Fishnet tool but I have encountered several issues. First, I have to put the cell height width and height as 0.004 rather than 400 even though the project measurement units are set as metres. Even when I do this, however, they are not 400 m x 400 m. Instead, all the cells are 375 m wide and 440 m tall when measured with the measure tool (geodesic).

I then attempted to create a grid manually using the reference grid as a guide. However, when I set the spacing of the reference grid to 400 m, the actual distance is around 380 m when measured with the measure tool (geodesic). 

My project CRS is GDA 1994.

Thanks for your help. 

[DavidPike]

GDA94 is the Datum and Spheroid for Australia I believe (from google i admit, UK here).  So your units are in decimal degrees - which is the issue. 

You'd need a planimetric coordinate system (MGA94 I believe).