Quite often I get the feedback that the map scale is wrong. A distance measured in the map made with Maproom differs from the same distance measured in Google Earth. How is this possible?
Projection
This is caused by the map projection. While map projections are quite complex and a huge topic to cover, you can think of them as the maths behind putting the Earth (a sphere) on a map (a flat plane). Or, how to flatten an orange peel. Both are impossible to achieve without some form of distortion. Luckily there are a lot of solutions to this problem in the form of map projections. Each map projection preserves some kind of aspect of the map, such as shapes, area, angles or distances or a combination. You can have a map where the distances measured from a point are accurate, but the shapes are off. Or you can have a map where the shapes look good but the areas are bad. It's always a compromise.
There are projections however which minimize these deviations for certain areas. For instance, when working on a city block it's best to pick the UTM projection in Maproom. When working on a global scale you could use Mollweide or Kavrayskiy.
Mercator projection
Mollweide projection
The projection Google uses (and all other online maps for that matter) is Mercator. It's a map projection from the late middle ages. It has one special property: straight lines on the map have a constant bearing. This is useful if you're sailing from Portugal to South America to find lots of gold and you're plotting the course on a map. Another property is that is heavily distorts shapes when you're not on the equator. From a contemporary mapping perspective the Mercator projection doesn't have much use, but hey: it's the standard! This distortion is mostly visible when you zoom out a lot. When you zoom in you can see square buildings are still square. But don't be fooled, the scale is still off.
You can see this issue in action with an experiment in Google Maps. Go to a location around the equator and then without zooming, pan either north or south. Keep a close look at the scale bar in the bottom right of the page. It changes while you pan around. Around the equator the scale is accurate, but moving away from the equator the scale is off.
The experiment: pan north starting at the equator. Don't zoom and watch the scale bar in the lower right corner.
Scale bars compared
Working with scale in Maproom
If you need to match the scale of drawings of buildings or infrastructure with your map, you're best served with the UTM projection. Find out how to change projection here. If you want to measure accurate distances on your map, regardless of the projection you're using you should add a Measure Path map layer. Read all about that here.