How Cadastral Maps Work: Understanding GIS, GeoJSON, and Digital Land Mapping
Have you ever wondered how digital maps represent individual plots of land, their boundaries, neighboring properties, and geographical locations? Behind these maps is a combination of technologies such as Geographic Information Systems (GIS), spatial databases, geospatial data formats, and map-rendering engines. One interesting application of these technologies is cadastral mapping — the process…
Cadastral maps represent individual land parcels and their boundaries using various technologies. These maps contain important details like parcel identification, land boundaries, geographical coordinates, land area, and ownership records. For example, in India, agricultural land parcels use Khasra or Gata numbers for identification.
Geographic Information Systems (GIS) enable digital land mapping by collecting, storing, processing, analyzing, and visualizing geographical data. GIS applications can combine multiple layers of information, including village boundaries, land parcels, roads, and administrative boundaries. Popular GIS tools include QGIS, PostGIS, GeoServer, Leaflet, and OpenLayers.
GeoJSON is a widely-used format for representing geographical data on the web. It supports geographical objects like points, lines, and polygons. A land parcel can be represented as a polygon within a GeoJSON feature. The polygon's coordinates define its geographical boundary, and the coordinates use the WGS84 coordinate reference system (longitude, latitude) with longitude appearing first.
Storing land parcel data efficiently is crucial for large-scale applications. PostgreSQL with PostGIS is a popular choice for this purpose. A simplified table structure for storing land parcels could include an ID, village ID, Khasra number, area, and boundary in the MultiPolygon geometry format. Creating a spatial index enhances query efficiency for geographical searches.
Finally, rendering land parcels on a web map involves using JavaScript libraries like Leaflet. This library can display GeoJSON polygons and attach click events to the parcels. By fetching land parcel data from a server and converting it into a Leaflet GeoJSON object, developers can create interactive maps that allow users to identify individual land parcels by clicking on them.
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