The first light blue number will be accumulated distance in metres from 0 on the grid. On the Columbia Icefield map it begins at 467000 metres east. The number increases by 1000 metres with each additional grid east. The grid system is quick simple and very accurate. This is the traditional system for global positioning.
Longitude is a series of imaginary lines radiating from the North and South poles.
There are 360 degrees of longitude. Latitude is a series of belts that circle the Earth. The equator is 0 degrees, and the north pole is 90 degreees north latitude. The border between western Canada and the United States is exactly 49 degrees north latitude. For both latitude and longitude, every degree is broken down into 60 minutes.