topic Re: Line Density Tool output cell size not equal to specified parameter in ArcGIS Pro Questions

Line Density Tool output cell size not equal to specified parameter

LaurieKurilla1 — Thu, 10 Dec 2020 03:18:18 GMT

I have created numerous line density maps of geologic faults with ArcGIS Pro Line Density tool. I specify a cell size and a search size. e.g. 5 and 25; 25 and 50 respectively and always specify output "area units" as 'square kilometers' . The resulting raster never has a unit cell size (5 or 25) that I specified. It is always considerably larger. The fault layer is WGS 1984 geographic coordinate.

Also, shouldn't the resulting unit output value (km/sq km) always be the same regardless of the cell size or search area size? I am getting different results for each run with different parameters.

Thank you
Laurie

Re: Line Density Tool output cell size not equal to specified parameter

DanPatterson — Thu, 10 Dec 2020 04:58:19 GMT

A lot can go wrong if you don't use projected data in the first place or forget to specify the projected output coordinate system in lieu of that. I would also have a look at the cell size projection method mentioned in the help topic since it will have an impact on the resultant raster.

Line Density (Spatial Analyst)—ArcGIS Pro | Documentation

My suggestion... project the raster first ensuring that you get cell sizes in meters squared, then run the line density tool

Re: Line Density Tool output cell size not equal to specified parameter

LaurieKurilla1 — Thu, 10 Dec 2020 22:07:26 GMT

Thank you Dan. I will review that documentation again and follow your
recommendations. Am I wrong in expecting the resulting unit density (km
per sq km) to be the same regardless of the cell and search size used?

Thank you
Laurie

Re: Line Density Tool output cell size not equal to specified parameter

DanPatterson — Thu, 10 Dec 2020 22:40:02 GMT

Laurie .... consider km per sq km to be a convenience expression. If your x, y and z values are in meters, then you expect the numeric expression to be proportional to converting area from m^2 to km^2 etcetera.

When you start mixing geographic coordinates and/or imperial/US units, I prefer to do the proper prep step and convert everything myself rather than rely on assumptions of conversion (unless you test yourself.)

Re: Line Density Tool output cell size not equal to specified parameter

LaurieKurilla1 — Thu, 10 Dec 2020 22:48:26 GMT

Dan,
Thank you for your prompt response. My question related to using different
cell and search sizes. For example, on one run I used 5 km output cell
size and 25 km search size. On another run I used 5 km cell size and 50 km
search size. Shouldn't both of these return the same unit density of x km
per sq km ?

Thanks
Laurie