41Latitude.com did a study on why Google Maps is a lot easier to read than most other maps. Google Maps labels tend to “pop” out more. In the animated GIF above, you will notice that the Yahoo! Maps screenshot is hard to read than the Google Maps screenshot. Its not the densities of the labels. There are three reasons why.
The first reason is that Google Maps uses thicker white outlines. This makes the background more obscure. The second reason is a greater number of label classes. This means that when you look at the Yahoo! Maps map and the Google Maps screenshots, you will notice four different font sizes on Google Maps and about three different font sizes on Yahoo! Maps.
And the last reason is because of lighter shadings on the lower classes of text. For example, the state label will be big and have a bolder shade. The big cities will be less bold, smaller font, and smaller outline. Cities that are smaller than that big city will have a smaller font, be less bold, be slightly lighter in black color, and will have a smaller outline. And then there is one more smaller class below that is lighter, less bold, smaller outlines, and smaller font.