Glossary

This section aims to summarize the terminology used in this application. It relates to geospatial terms, hydrology and environmental surveillance.

Basin

Also referred to as drainage basin, catchment area or watershed. This refers to a geographical area where all precipitation collects and drains into a common outlet. This can be a river, lake, reservoir, or other water body. In the context of this application, the site is the most relevant point in this regard.

Blue line

A digitized channel or stream, typically relevant for the sewage network and basin calculation. See also ‘Sewage line’.

Catchment

See basin. Note that on this application, the catchment of a site, however, also includes the underlying population and not only the area (i.e. the area polygon of the catchment is intersected with the underlying population raster to obtain a population for the catchment area).

DEM

Digital Elevation Model. A Digital Elevation Model is a digital representation of the Earth’s surface elevation. It consists of a grid of cells, where each cell (or pixel) contains a single elevation value, typically measured in meters above sea level. DEMs are used to model the topography of the land and are essential for hydrological and geomorphological analyses. Two subtypes are differentiated: 1) the Digital Terrain Model (DTM), that models the terrain elevation and 2) the Digital Surface Model (DSM), that models the surface of the Earth (ie buildings, trees etc).

Drainage line

This is one of the results of the hydrological processing. Above a certain water accumulation threshold (in pixels), a drainage line is drawn (see also Pixel accumulation threshold).

DSM

Digital Surface Model. See DEM.

DTM

Digital Terrain Model. See DEM.

Elevation raster

See DEM.

GIS

Abbreviation for a Geographical Information System.

Line features

In GIS, this refers to vectorial digital representation of lines. In the context of this application, these are rivers, sewage lines and barriers.

Point features

In GIS, this refers to vectorial digital representation of points. In the context of this application, these are sites.

Polygon features

In GIS, this refers to vectorial digital representation of polygons. In the context of this application, these are lakes and exclusion zones.

Population raster

A population raster is a type of spatial dataset in which population data is represented on a grid. Each cell (or pixel) in the raster contains a value indicating the estimated population count or density for the corresponding geographic area. Typically 100x100m in this application.

Raster

A raster refers to a data structure commonly used in GIS to represent spatial information. It consists of a grid of cells (also called pixels), where each cell contains a value representing information about a specific geographic location. In this application, we use population and elevation rasters.

Sewage line

In the context of this application, this refers to any digital representation of a channel, sewage flow, stream or river that is relevant for the sewage network and flow within the area of interest.

Snapping

Sites are snapped to a pixel to delineate their catchment. See Site snapping.

Stream burning

Digitized ground truth data is typically used to condition the DEM, i.e. improving the remote sourced data with the collected ground truth data. In this process, the digitized streams are ‘burned’ into the DEM. See Burning streams.

Trunk sewage line

A sewage line that does not have junctions with intersecting sewage lines. See Trunk lines.

Watershed

See basin.