How Scale Works
When you zoom in, the scale of the map increases (it gets larger). A large scale map covers a smaller land area than a small scale map. A map that is zoomed in to a small town is large scale, whereas a map of Canada is small scale.
This is rather counterintuitive. In fact, it confuses many people.
The explanation is that scale is a ratio. In other words, 1:10 means that one unit on the map represents ten units in the real world. In this case, the map is one-tenth the size of the real world. Because it is a ratio, it doesn't matter if the units are centimeters, miles, or any other units. If you have a 1:100 000 map, the map is 1/100 000 the size of the actual place. And if we remember our grade school math, 1/100 000 is a much smaller fraction (or ratio, or scale) than 1/10.
Basically, all you have to remember is this...
Larger scale equals greater detail.