I have a few thousands of GPS tracks (from and for recreational use) and I would like to sort those that were produced by a GPS on the field from those that were drawn (on-line on Google Earth or any other WebGIS or map editor such Garmin Basecamp or others).
Depending on the GPS settings and antenna, trackpoints are usually collected by time or distance to the log file before the final save. On many models this track is usually compressed (midle trackpoints are erased) to save memory space (I’m pretty sure that some of us still remember that the first affordable models use to have about 20 Mb of memory… enough to take you back or to load a few tracks or routes).
On my data set I have an average of trackpoints distance that goes from 1m to a maximum of 899m (Avg 45.80, Std 50.16).
I have compared this to 396 tracks collected by my Garmin Edge705 on Mountain Biking activities and the average trackpoint distance varied between 10m and 50m (Avg 28.89, Std 7.22). To optimize file size, sport models usually record a new point on every speed or trajectory change making huge variations between trakcpoints distance on the same track, but different models or settings could produce different results.
From my own data, it seems that average distances of up to 50 m could be considered as “collected on the field”, but I believe that GPS APPs for the current smartphones, or other models could push this value a little further… Within my dataset, tracks with average distance between trackpoints above 200 m are obviously drawn on a medium/small scale map on a WebGIS or other map software. Signs are easily spotted when these tracks are uploaded to a GIS – Tracks don’t usually follow the road, curves are not smooth as if they were collect on the field by a GPS handheld even taking into account GPS errors…
Above 100 m I still “feel” that most are drawn but what could be a reasonable value?