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perfect-postcode/pipeline/transform/test_crime_spatial.py

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import json
import numpy as np
import polars as pl
import pytest
import shapely
from pyproj import Transformer
from pipeline.transform.crime_spatial import transform_crime_spatial
from pipeline.transform.postcode_boundaries.loader import load_postcode_polygons
_TO_WGS84 = Transformer.from_crs("EPSG:27700", "EPSG:4326", always_xy=True)
_CSV_HEADER = (
"Crime ID,Month,Reported by,Falls within,Longitude,Latitude,Location,"
"LSOA code,LSOA name,Crime type,Last outcome category,Context"
)
def _bng_to_wgs84(x: float, y: float) -> tuple[float, float]:
lon, lat = _TO_WGS84.transform(x, y)
return lon, lat
def _square_feature(postcode: str, x0: float, y0: float, x1: float, y1: float) -> dict:
ring = [(x0, y0), (x1, y0), (x1, y1), (x0, y1), (x0, y0)]
coords = [list(_bng_to_wgs84(x, y)) for x, y in ring]
return {
"type": "Feature",
"properties": {"postcodes": postcode, "mapit_code": postcode.replace(" ", "")},
"geometry": {"type": "Polygon", "coordinates": [coords]},
}
def _write_boundaries(units_dir, features_by_district: dict[str, list[dict]]) -> None:
units_dir.mkdir(parents=True)
for district, features in features_by_district.items():
collection = {"type": "FeatureCollection", "features": features}
(units_dir / f"{district}.geojson").write_text(json.dumps(collection))
def _crime_row(month: str, x, y, crime_type: str) -> str:
if x is None or y is None:
lon, lat = "", ""
else:
lon, lat = _bng_to_wgs84(x, y)
return f",{month},F,F,{lon},{lat},On or near X,E01000001,L,{crime_type},U,"
def _write_month(
crime_dir, month: str, rows: list[str], force: str = "test-force"
) -> None:
"""Write one force's monthly CSV; an empty ``rows`` list still creates the
file, which counts as published coverage for that (force, month)."""
month_dir = crime_dir / month
month_dir.mkdir(parents=True, exist_ok=True)
body = "\n".join([_CSV_HEADER, *rows]) + "\n"
(month_dir / f"{month}-{force}-street.csv").write_text(body)
def _run(tmp_path, crime, units, **kwargs):
output = tmp_path / "crime_by_postcode.parquet"
by_year = tmp_path / "crime_by_postcode_by_year.parquet"
transform_crime_spatial(crime, units, output, by_year, buffer_m=50.0, **kwargs)
return pl.read_parquet(output), pl.read_parquet(by_year)
def test_buffer_overlap_counts_for_each_postcode(tmp_path):
units = tmp_path / "units"
# A and B sit 70m apart; their +50m buffers overlap in x in [1030, 1060].
_write_boundaries(
units,
{
"AB1": [
_square_feature("AB1 1AA", 1000, 1000, 1010, 1010),
_square_feature("AB1 1AB", 1080, 1000, 1090, 1010),
_square_feature("AB1 1AC", 5000, 5000, 5010, 5010),
]
},
)
crime = tmp_path / "crime"
_write_month(
crime,
"2024-01",
[
# In the overlap: 35m east of A, 35m west of B -> counts for both.
_crime_row("2024-01", 1045, 1005, "Burglary"),
# 49m east of C's edge -> inside C's buffer.
_crime_row("2024-01", 5059, 5005, "Robbery"),
# 51m east of C's edge -> outside every buffer.
_crime_row("2024-01", 5061, 5005, "Robbery"),
# No coordinate -> dropped entirely.
_crime_row("2024-01", None, None, "Anti-social behaviour"),
],
)
avg_df, _ = _run(tmp_path, crime, units)
rows = {r["postcode"]: r for r in avg_df.to_dicts()}
# Single covered month -> pooled rate x12.
assert rows["AB1 1AA"]["Burglary (avg/yr)"] == 12.0
assert rows["AB1 1AB"]["Burglary (avg/yr)"] == 12.0
assert rows["AB1 1AA"]["Robbery (avg/yr)"] == 0.0
# Only the 49m robbery counts for C; the 51m one and the blank row do not.
assert rows["AB1 1AC"]["Robbery (avg/yr)"] == 12.0
assert rows["AB1 1AC"]["Burglary (avg/yr)"] == 0.0
# Anti-social behaviour had no coordinate -> nobody gets it.
assert all(r["Anti-social behaviour (avg/yr)"] == 0.0 for r in rows.values())
def test_by_year_annualises_and_rolls_up(tmp_path):
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
# Point at the centre of AB1 1AA, well inside its buffer.
_write_month(
crime,
"2023-01",
[
_crime_row("2023-01", 1005, 1005, "Burglary"),
_crime_row("2023-01", 1005, 1005, "Robbery"),
],
)
_write_month(crime, "2024-01", [_crime_row("2024-01", 1005, 1005, "Burglary")])
_write_month(
crime,
"2024-02",
[
_crime_row("2024-02", 1005, 1005, "Burglary"),
_crime_row("2024-02", 1005, 1005, "Anti-social behaviour"),
],
)
_, by_year_df = _run(tmp_path, crime, units, min_bar_months=1)
assert by_year_df.height == 1
cols = set(by_year_df.columns)
assert {"Burglary (by year)", "Serious crime (by year)", "Minor crime (by year)"} <= cols
row = by_year_df.row(0, named=True)
burglary = sorted(row["Burglary (by year)"], key=lambda r: r["year"])
# 2023: 1 burglary in 1 covered month -> 12/yr; 2024: 2 in 2 months -> 12/yr.
assert burglary == [
{"year": 2023, "count": 12.0},
{"year": 2024, "count": 12.0},
]
serious = {p["year"]: p["count"] for p in row["Serious crime (by year)"]}
# 2023 serious = Burglary(12) + Robbery(12) = 24; 2024 = Burglary(12).
assert serious[2023] == 24.0
assert serious[2024] == 12.0
# Coverage calendar: both years published, with their month counts.
coverage = {c["year"]: c["months"] for c in row["covered_years"]}
assert coverage == {2023: 1, 2024: 2}
def test_area_normalisation_divides_out_buffered_catchment(tmp_path):
# Three postcodes of increasing footprint, each with exactly one incident in
# its buffer. Normalisation rescales by median_catchment / buffered_area, so
# the smallest scores highest and the median-sized one is unchanged -- i.e.
# the metric is a density. Dividing by the *buffered* catchment (not the raw
# polygon) means the fixed buffer-ring floor keeps the spread gentle, so the
# tiniest postcode is not blown up out of proportion.
units = tmp_path / "units"
_write_boundaries(
units,
{
"AB1": [
_square_feature("AB1 1AA", 1000, 1000, 1010, 1010), # 10x10
_square_feature("AB1 1AB", 3000, 3000, 3010, 3020), # 10x20 (median)
_square_feature("AB1 1AC", 5000, 5000, 5020, 5020), # 20x20
]
},
)
crime = tmp_path / "crime"
_write_month(
crime,
"2024-01",
[
_crime_row("2024-01", 1005, 1005, "Burglary"),
_crime_row("2024-01", 3005, 3010, "Burglary"),
_crime_row("2024-01", 5010, 5010, "Burglary"),
],
)
avg_df, by_year_df = _run(tmp_path, crime, units, min_bar_months=1)
# Re-derive the expected values from the same buffered catchment areas: each
# postcode is 12/yr before normalisation, then x (median_buf / buffered_area).
postcodes, polygons = load_postcode_polygons(units)
buf_area = {
pc: float(shapely.area(shapely.buffer(poly, 50.0, quad_segs=8)))
for pc, poly in zip(postcodes, polygons)
}
median_buf = float(np.median(list(buf_area.values())))
expected = {pc: 12.0 * median_buf / buf_area[pc] for pc in buf_area}
rows = {r["postcode"]: r for r in avg_df.to_dicts()}
for pc, exp in expected.items():
assert rows[pc]["Burglary (avg/yr)"] == pytest.approx(exp, abs=0.1)
# Median catchment unchanged; ordering is by inverse buffered area, but the
# buffer-ring floor keeps the spread far below the ~4x raw-area ratio.
assert rows["AB1 1AB"]["Burglary (avg/yr)"] == pytest.approx(12.0, abs=0.05)
small = rows["AB1 1AA"]["Burglary (avg/yr)"]
big = rows["AB1 1AC"]["Burglary (avg/yr)"]
assert small > 12.0 > big
assert small / big < 1.5
# by-year series carries the same normalisation.
small_row = by_year_df.filter(pl.col("postcode") == "AB1 1AA").row(0, named=True)
assert small_row["Burglary (by year)"] == [
{"year": 2024, "count": pytest.approx(expected["AB1 1AA"], abs=0.1)}
]
def test_avg_yr_is_pooled_rate_over_covered_months(tmp_path):
# Uneven month coverage across years: 2023 has 1 month (2 incidents),
# 2024 has 2 months (2 incidents). The headline is the POOLED annualised
# rate over all covered months: 4 incidents / 3 months * 12 = 16/yr -- not
# the old mean-of-bars (24+12)/2 = 18, which over-weighted thin years.
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
_write_month(
crime,
"2023-01",
[
_crime_row("2023-01", 1005, 1005, "Burglary"),
_crime_row("2023-01", 1005, 1005, "Burglary"),
],
)
_write_month(crime, "2024-01", [_crime_row("2024-01", 1005, 1005, "Burglary")])
_write_month(crime, "2024-02", [_crime_row("2024-02", 1005, 1005, "Burglary")])
avg_df, by_year_df = _run(tmp_path, crime, units, min_bar_months=1)
avg = avg_df.row(0, named=True)
assert avg["Burglary (avg/yr)"] == pytest.approx(16.0, abs=0.05)
# Bars remain per-year annualised: 2023 -> 24/yr (x12), 2024 -> 12/yr (x6).
row = by_year_df.row(0, named=True)
bars = {p["year"]: p["count"] for p in row["Burglary (by year)"]}
assert bars == {2023: pytest.approx(24.0, abs=0.05), 2024: pytest.approx(12.0, abs=0.05)}
def test_sporadic_type_is_not_inflated_by_years_present(tmp_path):
# A single robbery in a 24-covered-month window must read as ~0.5/yr (the
# long-run pooled rate), NOT 12/yr (the old years-with-incidents mean that
# inflated sporadic categories by up to ~15x).
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
for year in (2023, 2024):
for month in range(1, 13):
rows = []
if (year, month) == (2023, 6):
rows = [_crime_row(f"{year}-{month:02d}", 1005, 1005, "Robbery")]
_write_month(crime, f"{year}-{month:02d}", rows)
avg_df, by_year_df = _run(tmp_path, crime, units)
avg = avg_df.row(0, named=True)
# 1 incident over 24 covered months -> 0.5/yr.
assert avg["Robbery (avg/yr)"] == pytest.approx(0.5, abs=0.05)
# The by-year bar still shows the 2023 incident annualised over 12 covered
# months (1/yr); 2024 is covered with zero robberies -> no bar, but the
# year IS in the coverage list so consumers may render it as a true zero.
row = by_year_df.row(0, named=True)
bars = {p["year"]: p["count"] for p in row["Robbery (by year)"]}
assert bars == {2023: pytest.approx(1.0, abs=0.05)}
coverage = {c["year"]: c["months"] for c in row["covered_years"]}
assert coverage == {2023: 12, 2024: 12}
def test_force_gap_years_are_excluded_not_zeroed(tmp_path):
# Two postcodes policed by different forces. force-a publishes 2023+2024;
# force-b publishes only 2023 (a 2024 gap, like Greater Manchester). The
# b-postcode's headline must pool over force-b's 12 covered months only,
# and its by-year series must NOT contain a 2024 bar or coverage entry.
units = tmp_path / "units"
_write_boundaries(
units,
{
"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)],
"CD1": [_square_feature("CD1 1AA", 9000, 9000, 9010, 9010)],
},
)
crime = tmp_path / "crime"
for month in range(1, 13):
ym23 = f"2023-{month:02d}"
ym24 = f"2024-{month:02d}"
# force-a covers AB1 in both years; one burglary per month in 2024.
_write_month(crime, ym23, [], force="force-a")
_write_month(
crime, ym24, [_crime_row(ym24, 1005, 1005, "Burglary")], force="force-a"
)
# force-b covers CD1 in 2023 only: one burglary per month.
_write_month(
crime, ym23, [_crime_row(ym23, 9005, 9005, "Burglary")], force="force-b"
)
avg_df, by_year_df = _run(tmp_path, crime, units)
rows = {r["postcode"]: r for r in avg_df.to_dicts()}
# force-a postcode: 12 burglaries over 24 covered months -> 6/yr.
assert rows["AB1 1AA"]["Burglary (avg/yr)"] == pytest.approx(6.0, abs=0.05)
# force-b postcode: 12 burglaries over 12 covered months -> 12/yr. Under
# the old global calendar this would have been diluted to 6/yr by the
# uncovered 2024.
assert rows["CD1 1AA"]["Burglary (avg/yr)"] == pytest.approx(12.0, abs=0.05)
by_rows = {r["postcode"]: r for r in by_year_df.to_dicts()}
b_coverage = {c["year"]: c["months"] for c in by_rows["CD1 1AA"]["covered_years"]}
assert b_coverage == {2023: 12}
b_bars = {p["year"]: p["count"] for p in by_rows["CD1 1AA"]["Burglary (by year)"]}
assert set(b_bars) == {2023}
a_coverage = {c["year"]: c["months"] for c in by_rows["AB1 1AA"]["covered_years"]}
assert a_coverage == {2023: 12, 2024: 12}
def test_residue_incidents_in_uncovered_years_are_excluded(tmp_path):
# force-b stops publishing after 2023, but a force-a file contains a 2024
# incident that falls inside the b-postcode's buffer (cross-border residue,
# the Greater Manchester pattern). That incident must not produce a 2024
# bar for the b-postcode, nor leak into its pooled headline.
units = tmp_path / "units"
_write_boundaries(
units,
{
"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)],
"CD1": [_square_feature("CD1 1AA", 9000, 9000, 9010, 9010)],
},
)
crime = tmp_path / "crime"
for month in range(1, 13):
ym23 = f"2023-{month:02d}"
ym24 = f"2024-{month:02d}"
_write_month(crime, ym23, [], force="force-a")
# b's own 2023 incidents establish force-b as its home force.
_write_month(
crime,
ym23,
[_crime_row(ym23, 9005, 9005, "Burglary")] if month <= 6 else [],
force="force-b",
)
# 2024: only force-a publishes; one of its incidents lands in CD1 1AA.
_write_month(
crime,
ym24,
[_crime_row(ym24, 9005, 9005, "Burglary")] if month == 1 else [],
force="force-a",
)
avg_df, by_year_df = _run(tmp_path, crime, units)
b_row = avg_df.filter(pl.col("postcode") == "CD1 1AA").row(0, named=True)
# Pooled over force-b's 12 covered months (2023): 6 incidents -> 6/yr.
# The residue 2024 incident is excluded (force-b published 0 months in 2024).
assert b_row["Burglary (avg/yr)"] == pytest.approx(6.0, abs=0.05)
b_by = by_year_df.filter(pl.col("postcode") == "CD1 1AA").row(0, named=True)
bars = {p["year"]: p["count"] for p in b_by["Burglary (by year)"]}
assert set(bars) == {2023}
coverage = {c["year"]: c["months"] for c in b_by["covered_years"]}
assert coverage == {2023: 12}
def test_partial_years_below_min_bar_months_get_no_bar(tmp_path):
# 2023 fully covered; 2024 has only 2 published months. With the default
# 6-month minimum, 2024 must produce neither a bar (annualising x6 charts
# noise) nor a coverage entry -- but its incidents and months still count
# toward the pooled headline.
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
for month in range(1, 13):
ym = f"2023-{month:02d}"
_write_month(crime, ym, [_crime_row(ym, 1005, 1005, "Burglary")])
for month in (1, 2):
ym = f"2024-{month:02d}"
_write_month(crime, ym, [_crime_row(ym, 1005, 1005, "Burglary")])
avg_df, by_year_df = _run(tmp_path, crime, units)
# Pooled: 14 incidents over 14 covered months -> 12/yr.
assert avg_df.row(0, named=True)["Burglary (avg/yr)"] == pytest.approx(
12.0, abs=0.05
)
row = by_year_df.row(0, named=True)
bars = {p["year"]: p["count"] for p in row["Burglary (by year)"]}
assert set(bars) == {2023}
coverage = {c["year"]: c["months"] for c in row["covered_years"]}
assert coverage == {2023: 12}
def test_by_year_output_is_dense_with_coverage(tmp_path):
# A postcode with zero incidents still gets a by-year row carrying its
# coverage calendar, so "covered and crime-free" is distinguishable from
# "no data" downstream.
units = tmp_path / "units"
_write_boundaries(
units,
{
"AB1": [
_square_feature("AB1 1AA", 1000, 1000, 1010, 1010),
_square_feature("AB1 1AB", 5000, 5000, 5010, 5010),
]
},
)
crime = tmp_path / "crime"
_write_month(crime, "2024-01", [_crime_row("2024-01", 1005, 1005, "Burglary")])
avg_df, by_year_df = _run(tmp_path, crime, units, min_bar_months=1)
assert by_year_df.height == 2
quiet = by_year_df.filter(pl.col("postcode") == "AB1 1AB").row(0, named=True)
assert quiet["Burglary (by year)"] is None
assert [c["year"] for c in quiet["covered_years"]] == [2024]
# And the headline for the quiet postcode is a genuine 0, not null.
quiet_avg = avg_df.filter(pl.col("postcode") == "AB1 1AB").row(0, named=True)
assert quiet_avg["Burglary (avg/yr)"] == 0.0
def test_serious_rollup_avg_yr_equals_sum_of_components(tmp_path):
# Burglary only in 2014, Robbery only in 2024 (one incident each, 2 covered
# months total). Components pool over the same covered window (each
# 1 x 12 / 2 = 6/yr) and the rollup equals their sum.
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
_write_month(crime, "2014-01", [_crime_row("2014-01", 1005, 1005, "Burglary")])
_write_month(crime, "2024-01", [_crime_row("2024-01", 1005, 1005, "Robbery")])
avg_df, by_year_df = _run(tmp_path, crime, units, min_bar_months=1)
avg = avg_df.row(0, named=True)
assert avg["Burglary (avg/yr)"] == pytest.approx(6.0, abs=0.05)
assert avg["Robbery (avg/yr)"] == pytest.approx(6.0, abs=0.05)
# Rollup == sum of its component (avg/yr) columns.
assert avg["Serious crime (avg/yr)"] == pytest.approx(12.0, abs=0.05)
assert avg["Serious crime (avg/yr)"] == pytest.approx(
avg["Burglary (avg/yr)"] + avg["Robbery (avg/yr)"], abs=0.05
)
# The by-year rollup series remains the per-year sum of the component bars.
serious_bars = {
p["year"]: p["count"]
for p in by_year_df.row(0, named=True)["Serious crime (by year)"]
}
assert serious_bars == {
2014: pytest.approx(12.0, abs=0.05),
2024: pytest.approx(12.0, abs=0.05),
}
def test_unknown_crime_type_is_dropped_with_warning(tmp_path, capsys):
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
_write_month(
crime,
"2024-01",
[
_crime_row("2024-01", 1005, 1005, "Burglary"),
_crime_row("2024-01", 1005, 1005, "Cyber fraud"),
],
)
avg_df, _ = _run(tmp_path, crime, units)
columns = avg_df.columns
# The unknown type is dropped (no column for it) but a warning is emitted.
assert "Cyber fraud (avg/yr)" not in columns
assert "Burglary (avg/yr)" in columns
err = capsys.readouterr().err
assert "Cyber fraud" in err
assert "WARNING" in err
def test_legacy_crime_types_are_mapped(tmp_path):
"""Pre-2014 crime-type names are aliased to current equivalents in the
spatial transform instead of being dropped as unknown types."""
units = tmp_path / "units"
_write_boundaries(
units, {"AB1": [_square_feature("AB1 1AA", 1000, 1000, 1010, 1010)]}
)
crime = tmp_path / "crime"
_write_month(
crime,
"2013-01",
[
_crime_row("2013-01", 1005, 1005, "Violent crime"),
_crime_row("2013-01", 1005, 1005, "Public disorder and weapons"),
],
)
avg_df, by_year_df = _run(tmp_path, crime, units, min_bar_months=1)
row = avg_df.to_dicts()[0]
# Single postcode -> area-norm factor 1.0; single covered month -> x12.
assert row["Violence and sexual offences (avg/yr)"] == 12.0
assert row["Public order (avg/yr)"] == 12.0
by_year_row = by_year_df.row(0, named=True)
assert by_year_row["Violence and sexual offences (by year)"] == [
{"year": 2013, "count": 12.0}
]
assert by_year_row["Public order (by year)"] == [{"year": 2013, "count": 12.0}]
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