Google Earth and Google Maps are great, but not perfect

I have absolutely no desire to bash Google Maps and Google Earth. I believe that these products have totally revolutionized the way we plan trips, and I like them a lot. Still, there are some things you need to be aware of, especially if dealing with hilly or mountainous terrain.

There are three types of roads in Google Maps and Google Earth:

1. those Google "knows about" and uses in driving directions;
2. ones that Google "knows about", but does not use in driving directions (those are usually minor roads; they are often dead ends, or Google "thinks" that they are);
3. and, finally, roads that Google "doesn't know about" plus roads that are not really full-blown roads, but rather paths (sometimes drivable and sometimes not) in the woods, fields, pastures, etc.

The first two types of roads have "road labels" (lines on the map that, with some degree of approximation, follow the actual roads). The third one, obviously, does not.

If you are like me, you probably use the "snap to roads" option whenever possible in Google Maps. It saves a lot of time compared to actually drawing lines by hand. I draw lines by hand only when I have to deal with "roads of type 3".

In Google Maps, if you have ever zoomed in really close (say, to the 1 inch = 500 ft scale or closer) in the "Satellite" mode with labels on, you might have notices that the lines showing roads (road labels) are not exactly where the actual roads are on the satellite image (it is even more noticeable in Google Earth since you can often zoom in much closer). The problem is that with the "snap to roads" option on, the lines you draw do not snap to the actual roads, but to the road labels instead. It is probably not such a big deal if you drive. It might even be acceptable if you ride a bicycle as long as it is not a mountain route, and you don't really care much about the accuracy of its vertical profile. In the mountains, however, a couple of feet off the road may actually be a vertical wall, and that will mess up the values of the steepest slopes, as well as - to some extent - the average gradients. The highest and the lowest elevation values should not be affected that much (unless you are going to traverse some really steep mountain slopes).

So, here are the conclusions:

• if you need more accurate vertical profiles,
• draw your routes by hand in the "Satellite" mode in Google Maps or, better yet, in Google Earth;
• make sure you zoom in really close and follow the actual roads - not the streamlined road labels;
• keep in mind that Google Earth vertical profile will hardly ever be 100% accurate.