OpenStreetMap history — building footprints over time (ohsome)¶

This notebook teaches the ohsome half of the earthlens.osm backend: OSM is history-aware, so you can ask what the map looked like at a point in time. We pull building footprints for two yearly snapshots of the same area and compare them.

Like the Overpass path, ohsome returns a vector FeatureCollection (EPSG:4326) and emits the ODbL LicenseWarning. Unlike Overpass, an ohsome query needs a time (start= / end=).

Setup¶

Imports and a small output directory. The same tiny Heidelberg bbox as the quickstart.

In [ ]:

from pathlib import Path

import matplotlib.pyplot as plt

from earthlens.core import EarthLens

OUT_DIR = Path('osm_output')
OUT_DIR.mkdir(exist_ok=True)
LAT_LIM = [49.40, 49.42]
LON_LIM = [8.67, 8.71]

from pathlib import Path import matplotlib.pyplot as plt from earthlens.core import EarthLens OUT_DIR = Path('osm_output') OUT_DIR.mkdir(exist_ok=True) LAT_LIM = [49.40, 49.42] LON_LIM = [8.67, 8.71]

A single historical snapshot¶

ohsome:buildings returns building footprints as they existed at the start date. ohsome's own columns ride along: @osmId (the element id) and @snapshotTimestamp (the snapshot instant). Here we ask for the state on 1 January 2018.

In [ ]:

buildings_2018 = EarthLens(
    data_source='osm',
    variables=['ohsome:buildings'],
    lat_lim=LAT_LIM,
    lon_lim=LON_LIM,
    start='2018-01-01',
    path=str(OUT_DIR),
).download()

len(buildings_2018), buildings_2018['@snapshotTimestamp'].iloc[0]

buildings_2018 = EarthLens( data_source='osm', variables=['ohsome:buildings'], lat_lim=LAT_LIM, lon_lim=LON_LIM, start='2018-01-01', path=str(OUT_DIR), ).download() len(buildings_2018), buildings_2018['@snapshotTimestamp'].iloc[0]

Map the 2018 footprints¶

The footprints are polygons; plot them filled.

In [ ]:

ax = buildings_2018.plot(
    facecolor='#9ecae1', edgecolor='#3182bd', linewidth=0.3, figsize=(7, 6)
)
ax.set_title(f'{len(buildings_2018)} building footprints — 2018-01-01 (ohsome)')
ax.set_xlabel('longitude')
ax.set_ylabel('latitude')
plt.show()

ax = buildings_2018.plot( facecolor='#9ecae1', edgecolor='#3182bd', linewidth=0.3, figsize=(7, 6) ) ax.set_title(f'{len(buildings_2018)} building footprints — 2018-01-01 (ohsome)') ax.set_xlabel('longitude') ax.set_ylabel('latitude') plt.show()

Compare two snapshots — how the map grew¶

Because ohsome is history-aware, the same query at a later date shows how mapping progressed. We pull the 2023 snapshot and compare the building counts — OSM coverage grows over time as contributors add detail.

In [ ]:

buildings_2023 = EarthLens(
    data_source='osm',
    variables=['ohsome:buildings'],
    lat_lim=LAT_LIM,
    lon_lim=LON_LIM,
    start='2023-01-01',
    path=str(OUT_DIR),
).download()

counts = {'2018': len(buildings_2018), '2023': len(buildings_2023)}
counts

buildings_2023 = EarthLens( data_source='osm', variables=['ohsome:buildings'], lat_lim=LAT_LIM, lon_lim=LON_LIM, start='2023-01-01', path=str(OUT_DIR), ).download() counts = {'2018': len(buildings_2018), '2023': len(buildings_2023)} counts

A quick bar chart makes the growth between the two snapshots legible.

In [ ]:

fig, ax = plt.subplots(figsize=(4, 4))
ax.bar(list(counts), list(counts.values()), color=['#9ecae1', '#3182bd'])
ax.set_title('Mapped building footprints, same bbox')
ax.set_ylabel('feature count')
plt.show()

fig, ax = plt.subplots(figsize=(4, 4)) ax.bar(list(counts), list(counts.values()), color=['#9ecae1', '#3182bd']) ax.set_title('Mapped building footprints, same bbox') ax.set_ylabel('feature count') plt.show()

Raw ohsome filter (power users)¶

Pass your own ohsome filter via filter= to query any tag combination — here, parks (leisure=park) as polygons at the 2023 snapshot.

In [ ]:

parks = EarthLens(
    data_source='osm',
    variables=['ohsome:buildings'],  # still required to route to ohsome
    lat_lim=LAT_LIM,
    lon_lim=LON_LIM,
    start='2023-01-01',
    filter='leisure=park and geometry:polygon',
    path=str(OUT_DIR),
).download()

len(parks)

parks = EarthLens( data_source='osm', variables=['ohsome:buildings'], # still required to route to ohsome lat_lim=LAT_LIM, lon_lim=LON_LIM, start='2023-01-01', filter='leisure=park and geometry:polygon', path=str(OUT_DIR), ).download() len(parks)

Takeaway¶

• ohsome adds a time axis to OSM: pass start= (and optionally end=) to get the map as it was, or a range.
• The result carries @osmId / @snapshotTimestamp so you can track features across time.
• A raw filter= queries any tag combination; the ODbL obligation applies to ohsome data too.

See quickstart.ipynb for the current-state Overpass protocol.