The various dots on your map help you distinguish between GPS accuracy and a location that has been provided using the backup location estimation service. Therefore we have used colour to help achieve that.
Simply put
Green = GPS = Highest Accuracy
Blue = Location estimation only = Medium Accuracy
Red = Location estimation only = Lowest Accuracy
It is best to really understand how to get the best GPS signal and to get a handle of the backup location service. To do so, we recommend reading the following article.
Positioning your GPS to get the best signal and using Cellular location