OSM Feature Coverage Diagnostic

1 Overall coverage

column n_links n_filled pct_coverage
is_unpaved 2167557 350597 16.2
lanes 2167557 158217 7.3
lit 2167557 201442 9.3
speed_limit_mph 2167557 1223142 56.4

2 Coverage by road class (%)

column Motorway A Road B Road Classified Unnumbered Unclassified Not Classified Unknown
is_unpaved 36.2 27.4 24.9 20.2 16.7 12.5 9.2
lanes 40.3 34.7 21.9 13.2 4.4 1.9 1.5
lit 38 25 16.4 10.8 10.1 3.6 2.3
speed_limit_mph 46.1 55.3 52.4 53.9 59.4 57.4 51.1

3 Coverage by latitude band (%)

column 51–52°N 52–53°N 53–54°N 54–55°N 55–56°N
is_unpaved 2.7 22.4 13.7 17.2 8.9
lanes 1.2 10.2 5.6 9.2 4.3
lit 1.2 11.3 8.2 12.1 8.5
speed_limit_mph 10.8 75 47.8 66 36.2

4 Value distributions (populated rows only)

4.1 speed_limit_mph

road_class n_filled n_distinct min q25 median q75 max
Motorway 1882 32 15 70 70 70 70
A Road 86016 65 10 30 36 50 115
B Road 46830 58 10 30 30 40 125
Classified Unnumbered 102922 61 10 30 33 40 195
Unclassified 630118 74 6 22 26 30 220
Not Classified 129078 62 6 21 25 29 224
Unknown 226296 76 6 20 22 26 224

4.2 lanes

road_class n_filled n_distinct min q25 median q75 max
Motorway 1644 8 1 2 2 3 10
A Road 53962 7 1 2 2 2 8
B Road 19547 7 1 2 2 2 7
Classified Unnumbered 25119 6 0 2 2 2 5
Unclassified 47151 7 0 2 2 2 20
Not Classified 4347 6 0 1 2 2 5
Unknown 6447 6 1 1 2 2 6

5 Highlights

5.1 Columns with >80% coverage by road class (usable without imputation)

No column × road-class combination reaches 80% coverage.

5.2 Columns with <20% coverage by road class (imputation would invent most values)

road_class column pct_coverage n_links n_filled
Unknown lanes 1.5 442836 6447
Not Classified lanes 1.9 224878 4347
Unknown lit 2.3 442836 10265
Not Classified lit 3.6 224878 8139
Unclassified lanes 4.4 1060014 47151
Unknown is_unpaved 9.2 442836 40849
Unclassified lit 10.1 1060014 107342
Classified Unnumbered lit 10.8 190921 20620
Not Classified is_unpaved 12.5 224878 28159
Classified Unnumbered lanes 13.2 190921 25119
B Road lit 16.4 89286 14618
Unclassified is_unpaved 16.7 1060014 176644

5.3 Decision guidance

For each column × road-class, coverage determines the right modelling strategy:

  • ≥80%: Include as-is; drop the small fraction of missing rows.
  • 20–80%: Median-impute and add an {col}_imputed binary flag; coefficient reflects the imputed value and should be interpreted with caution.
  • <20%: The imputed value is invented for >80% of rows. The coefficient will primarily reflect the imputation default, not genuine signal. Consider excluding from the model or using road-class median as a proxy only if the proxy is defensible.

Note: coverage on major roads (Motorway, A Road) is typically higher because OSM contributors prioritise high-traffic routes. If those columns are included in a model trained on all road classes, the signal comes almost entirely from major roads and the imputed values for minor roads are close to noise.