Half-mile’s maps of the PCT have an unusual scale: 1:31,680, so that one inch on the map equals a half mile on the ground.
Like any decent map they have UTM coordinates on them, so you can find where you are if you have those coordinates. I use the MilGPS iOS app on my phone for that.
MapTools is the site I first used to get me into UTM format and how to use it. I can do math based on tens much easier that our clung-to clumsiness of the sexagesimal math of the Babylonians.
But UTM grids on maps are still a kilometer wide. Sometimes, I like to have a bit more accuracy than that when looking at the map (and estimating). That’s where grid tools come in.
The basic function of the grid tool is to extend the precision of your map to match your GPS UTM coordinate more closely.
The grid tools they make are simple to use. It is a small plastic square that you place on the map over the grid you are located within, and then it allows you to pinpoint your location to within the grid to within a hundred (or less) meters of accuracy.
The grid tool must of course match the scale of your map and Maptools makes a grid overlay tool for the uncommon 1:31,680 scale of the Pacific Crest Trails maps made by Half-mile.
And at 4.5 grams, while I admit it’s more of a WANT than a NEED, given my style of on trail hiking an eyeball estimation within that square kilometer is usually close enough to know where I am on the trail, I do enjoy my maps and navigation, so it’s light enough to take. And of course, when you are off-trail, location specificity can be vital.