The location service is transparent and extracts the data from the network operator as to the location of the mobile that you want to track. In essence, we get the same data as the police regarding the movement and location of mobiles.
Mobile phone tracking is not an exact science and accuracy will vary depending upon the cell mast density of the area that the mobile is within.
We have seen mobile phone accuracy as precise as 100m in central London (where there are many cell masts) and as inaccurate as 10km in the Scottish Highlands(where there are few cell masts).
We have also seen fluctuations where a local cell mast is down or overloaded with calls, when you requested a location. This can result in the mobile phone being logged onto a longer range mast by your network operator and accuracy in such cases can diminish. However, the movement of the phone throughout the day to differing locations will minimise any user experience effected by network failures/overloads in specific area.
When looking at the map, remember that the mobile phone location is likely to be on the outer edge of the orange circle.