I have a table of geocoded pupils and a layer with a polygon representing my city boundary. I need to find how many pupils are located 20 miles or more outside of the city boundary.
I've been reading and i think this could possible be achieved by creating a buffer of 20 miles around the city boundary polygon and then using the SQL Select to query the data to find the points within the polygon which would allow me to determine which pupils fall outside of it.
I have calculated points within a polygon before using this method but I've never created a buffer. I would like to know how i can create the type of buffer which would make a polygon which is the same shape as my city but 20 miles distance from each of the nodes.
Is this an approach i should be taking or should i be doing this a different way?