Glossary¶
Key terms used in the course, explained for planners.
- Band
- One layer of a satellite image, recording one colour of light (for example red, or near-infrared). A colour photo has three bands. Sentinel-2 has thirteen.
- Bounding box (bbox)
- The rectangle that encloses an area, written as four numbers: west, south, east, north.
- Centroid
- The centre point of a shape.
- Circuity
- How much longer a route along the streets is than the straight-line distance. A value of 1.0 means the streets are perfectly direct.
- CRS (Coordinate Reference System)
- The system used to give locations coordinates. Latitude and longitude (EPSG:4326) are good for storing data. A projected CRS such as UTM zone 43N (EPSG:32643) is used for measuring distances and areas in metres around Bengaluru.
- DEM (Digital Elevation Model)
- A raster where each pixel holds the ground height above sea level.
- Footprint
- The outline of a building on the ground, stored as a polygon.
- GeoDataFrame
- A table (like a spreadsheet) where each row also has a shape: a point, line or polygon. It comes from the GeoPandas package.
- Ground coverage
- The share of a plot or area covered by building footprints, in percent.
- Intersection density
- The number of street intersections per square kilometre. Higher values usually mean smaller blocks and a more walkable area.
- Isochrone
- The area you can reach from a point within a set time, for example a 15-minute walk.
- Land cover
- What physically covers the ground: trees, water, buildings, bare soil. It differs from land use, which is what people use the land for.
- LST (Land Surface Temperature)
- How hot the ground surface is, measured by a satellite's thermal sensor. On a sunny day it is often much hotter than the air temperature.
- NDBI (Normalised Difference Built-up Index)
- A satellite index that highlights built-up areas. It is calculated from short-wave infrared and near-infrared bands.
- NDVI (Normalised Difference Vegetation Index)
- A satellite index that measures how green and healthy vegetation is. It ranges from -1 to 1, and values above about 0.4 usually mean dense vegetation.
- Network graph
- A street network stored as nodes (intersections) and edges (street segments between them).
- OpenStreetMap (OSM)
- A free, editable map of the world built by volunteers, like a Wikipedia for maps.
- Pixel / resolution
- The smallest square in a raster. "10 m resolution" means each pixel covers 10 m by 10 m on the ground.
- Random Forest
- A machine learning method that learns from labelled examples and then predicts labels for new data. It works by combining many simple decision trees.
- Raster
- Data stored as a grid of pixels, like a photo. Satellite images and elevation models are rasters.
- Remote sensing
- Collecting information about the Earth from a distance, usually with satellites or drones.
- Slope
- How steep the ground is, in degrees.
- STAC (SpatioTemporal Asset Catalog)
- A standard way to search catalogues of satellite images by place, date and cloud cover.
- Suitability analysis
- Combining several map layers, each given a weight, to score how suitable every location is for a use.
- Vector
- Data stored as points, lines and polygons, for example bus stops, roads and building footprints.
- Zonal statistics
- Summarising raster values inside each zone, for example the average NDVI in each ward.