In order for NetSpot to accurately map the Wi-Fi signals in your space, it needs to know the actual distance between points. You also need to be able to accurately locate yourself on the map each time you stop for a scan. Providing a map drawn to scale gives NetSpot the measurements it needs. A nice map also results in a professional-looking heatmap that can be submitted in a report, if needed.
If you don’t have a map, see “How do I create and save a map of my area?” for ideas on how to create one.