To get the distance Equilab measures the total length of the path of the map. Therefore if the path on the map looks incorrect as well look at section about the path not being registered correctly.
It is shorter/longer than other running apps
The raw locations that gets reported from the hardware in your phone includes data points that often is of very low accuracy and not on the path you are riding. Apps like Equilab therefore filter away these before presenting the data for you. How these are filtered are a little bit different depending on apps though. Since Equilab is built for equestrians the focus has been to make it as correct as possible for riders and get as close to the "real" distance as possible.
Some of the primary differences between between different apps is how they handle:
- Locations reported when you are standing still. Equilab tries to removes all these points
- You are indoor. Equilab tries to only include real points when this is the case
- How much to smooth the path. This is a more complex question, for those interested it has to do with the mathematical problem of the coastline paradox.
These are the reason some apps gives a longer distance and some shorter, it is not super uncommon to be more than a km difference between two apps. However, as long as you are using one of the big ones such as Strava, Garmin, Endomondo, Runkeeper or Equilab the distance you are getting should be as correct as it can get. It is more a question of how what you prefer is done in the different cases.