Maybe this is obvious but Hunting Pressure will also go up if you shoot/kill any animals in that zone. It will eventually go back down again if you avoid the area. Basically you're better off avoiding any areas showing a high Pressure number as animals will be avoiding it too.
Presence, using the clock indicator, tells you at what time of day the animals are likely to be in that area. You can also tell by a faint glowing outline around the icon showing what type of area it is (water, food or bedding) denoting an active area.
Another thing that's never explained is a dot or X on the map - but if you hover your mouse on one it will tell you - I think dot is where you shot the animal, X is where you Claimed your Trophy (or maybe the other way 'round).