Reference

Last updated on 2026-10-17 | Edit this page

Glossary

API (Application Programming Interface)
A web address that returns data to a program instead of a web page. The Census data API and the Overpass API are examples.
Census tract
A small statistical area defined by the U.S. Census Bureau, usually with 1,200 to 8,000 people.
Coordinate Reference System (CRS)
The system that links coordinates to places on Earth. EPSG:4326 is latitude and longitude; UTM zones (such as EPSG:32616) use meters.
DBSCAN
A density based clustering method that groups points with many neighbors within a radius (eps) and labels isolated points as noise.
Edge
In a network, a connection between two nodes. In a road network, a road segment.
GeoDataFrame
A pandas DataFrame with a geometry column, provided by GeoPandas.
HDBSCAN
A version of DBSCAN that tests many distances and keeps stable clusters, so you do not choose eps.
K-Means
A clustering method that splits points into a chosen number (k) of groups around central points.
LISA (Local Indicators of Spatial Association)
Local Moran’s I values for each place, used to map hotspots (High-High), coldspots (Low-Low) and outliers.
Moran’s I
A statistic that measures spatial autocorrelation: positive when similar values are near each other, near zero when there is no pattern.
NDVI (Normalized Difference Vegetation Index)
(NIR - Red) / (NIR + Red), a measure of vegetation greenness from satellite bands.
Near infrared (NIR)
Light just beyond what the eye can see. Healthy vegetation reflects it strongly.
Node
In a network, a point where edges meet. In a road network, an intersection or dead end.
OpenStreetMap (OSM)
A free, volunteer built map of the world. Features are described by key=value tags such as shop=supermarket.
Overpass API
The query service used to search and download OpenStreetMap data.
Permutation test
A significance test that shuffles values many times to see how often a result as strong as the real one appears by chance. Its result is a pseudo p-value (p_sim).
Projection (reprojecting)
Converting data from one CRS to another, for example from degrees to meters with to_crs().
Raster
A grid of cells (pixels), each holding a value. Satellite images and elevation models are rasters.
Rate limit
The maximum number of requests a web service accepts in a period, for example one per second.
Reflectance
The share of incoming light a surface reflects, from 0 to 1.
Spatial autocorrelation
The tendency of nearby places to have similar (positive) or different (negative) values.
Spatial weights (W)
A record of which places are neighbors. Common types are Rook, Queen and K-nearest neighbors.
Vector data
Data stored as points, lines or polygons, such as addresses, roads or county boundaries.

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