Map: 12 fingerprints, 2 walks over 1 stretches, 2 outings.

Each outing held out in turn, and its scans located from the other outings:

                                by networks  and by signal  settling ties choosing the path
  scans held out                         12             12             12                12
  placed on the right stretch            12             12             12                12
  placed across a mark                    0              0              0                 0
  landed on the wrong stretch             0              0              0                 0
  not on the map                          0              0              0                 0
  mean error, of a stretch               7%             2%             7%                7%
  median error, of a stretch             5%             2%             5%                5%
  mean error in metres                 10 m            3 m           10 m              10 m
  median error in metres                7 m            3 m            7 m               7 m

  A scan that landed on the wrong stretch is not a small error, it is a different street,
  so it is counted apart rather than averaged into the distances. One placed across a mark
  is on the stretch next door, a few metres past the mark the two share, and its error is
  measured through that mark. Settling ties places each scan with the scans before it
  breaking a tie between two stretches. Choosing the path takes the likeliest path through
  them, which can overrule the scan itself.
