What do the blue numbers mean that are placed around the edge of the map?
These are UTM (Univeral Tranverse Mercator) numbers, which are an alternate grid to Latitude-Longitude. For comparison purposes, think of the metric system of metres and kilometres compared to the English system of feet and inches. The UTM grid is easier to use once you get the hang of it, and more acurate, because the divisions are all in tens. Try searching the internet for some information about how the grid works and how to define points on the grid (grid references). You can easily set your GPS to operate in Lat-Long or in UTM, similar to selecting miles or kilometres.
