Mapsofts don't normally come in ratings, this is true. This is also something I've always felt was an error, because virtually everything else in the system has a rating. When you're trying to figure out where you are, compare a national or state map with a city map, with a USGS survey map - or architectural plans. The more detailed the map, the higher the rating, the better off you can be in regards to determining which way you want to go: ratings. Doing maps, mapsofts (which are just specific datasofts), and area-knowledge knowsofts in this manner reflects the skill rating system.
In addition, the more specific you get, the more and different details you'll have - compare and contrast a rating 1 'Seattle Metroplex' map with a rating 6 'ACHE, Floors 200-220' architectural plan. On the former you'll have major roads and freeways, with cities laid out, and maybe the ACHE labelled as a major point of interest. On the latter you won't have any of the former, but you'll know where the water, power, network, and sewer lines are. Compare those datasofts with a relatively high-rated knowsoft of the latter - you don't have to figure out how to get from A to B, you KNOW the shortcuts you need to take to get there ahead of the opposition, or exactly what consequence you're going to have if you put the cutting charge here instead of there - a blast of stinky sewage, as compared to a power outage.