# Change map unit for focal statistics

I have around 1000 GPS Points and want to calculate the average value of Night lights, within a 10 km radius in ArcGis. My first approach was to do this with buffers, but a lot of polygons overlap and Zonal Statistics is problematic. Which is why I decided to solve it with Focal Statistics. My approach would be:

1) Focal statistics with a 10 km radius

2) Extract Values to Points to get the respective value

However, when using Focal Statistics, I cannot specify kilometers (as I could for Buffers). Instead I have to specify the amount of map units of the radius. After reading through several forum posts, I figured that I somehow have to change the projection to a system where linear units (meters) are used. Is that correct? And if so, how do I know which one is the appropriate, as there are many systems that use meter? (Night lights have a CGS_WGS_1984 coordinate system).

• This is really a projection problem, you need to project your data into a "local" coordinate system using metres as units. You don't say which country you are working on, so nobody can comment on the best choice. Suggest you look at spatialreference.org – Hornbydd Mar 13 '17 at 16:32
• @Hornbydd Thanks and sorry I forgot to mention that I work on Egypt and the locations are distributed all over Egypt (but a lot overlap with 10 km buffers). What criteria to use for my choice? Is there any good site where I could find information when to choose which projection? – SpanishTrain Mar 13 '17 at 18:12
• Have a look at this website. – Hornbydd Mar 13 '17 at 19:17