Road Geometry Mapping: Balancing between GPS Traces and Imagery Alignment

I haven’t come across any comprehensive documentation detailing the precise mapping guidelines for road geometry. Therefore, I would greatly appreciate any input or feedback on this matter.

This message is in continuation of the discussion from: Strava: mapping legal usage - #34 by dieterdreist

In practice, visible roads are often initially mapped using imagery alone, and later adjusted using GPS data if available.

It is widely recognized that GPS accuracy can be limited in areas with dense forest cover or mountainous terrains due to weak signal reception (drifts).

However, relying solely on imagery for alignment poses its own challenges, as it can have inherent offset issues that make it unreliable.

While I haven’t found official statistics, I believe that navigation and routing constitute the primary use-case for OpenStreetMap data. Considering this, I tend to prioritize, in mountainous and remote areas, quality averaged out GPS-traced geometry (e.g. Strava) over imagery alone.

Since satellite imagery is typically not visible to end-users in their applications, the limitations of GPS accuracy may go unnoticed. Conversely, if a road aligns with the imagery but deviates from the averaged GPS traces in an area with known accuracy issues, it may lead to complaints about poor map quality from end-users.

The main drawback of favoring GPS-traced geometry is that mappers may encounter conflicting road alignments that do not match the available imagery. However, it is important to acknowledge that imagery itself may not always represent the ground truth accurately due to offset issues.

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