Vector data model

Also called: Vector format · Topic: Remote Sensing, GIS and GNSS · NCERT: Class 12, Ch 4 "Spatial Information Technology"

Meaning

The vector data model is a way a GIS (Geographic Information System, a computer system that stores and studies data tied to places) stores the location of features as points, lines and polygons built from real coordinates: (x, y), or (x, y, z) when height is added. It matters because it is the best format for discrete features with clear boundaries, such as roads, rivers and districts. It gives compact files and precise maps, and it can record how features are connected.

Explanation

How it works: three building blocks

• Every feature is stored as points with real coordinates, not as grid cells.
• (x, y) gives a position on the map.

• (x, y, z) adds height.

• Point: one coordinate pair.

• Example: a well, or a town shown on a small-scale map.

• Line: an ordered list of points joined one after another.

• Example: a road, river or railway.

• Polygon: a closed chain of ordered points that surrounds an area.

• Example: a district or a lake.

• The descriptive part (name, population, soil type) is kept separately as attribute data in tables. Each feature is linked to its own row in the table.

Topology: recorded relationships

• Topology: the relationships between features, stored by the GIS. It is a feature of the vector model.
• Connectivity (connection): which lines join. Example: which roads meet at a junction.
• Adjacency: which areas share a border. Example: two neighbouring districts.

• Containment: which features lie inside others. Example: a village inside a tehsil.

• Topology is built only after errors are corrected.

• A gap or an overshoot would create false links.
• So the data is checked and edited first, and topology is built after that.

How vector data is made: digitisation

• Digitisation: tracing map features into x, y coordinates.
• It is done by hand on a digitising tablet, or on screen over a scanned image.

• It is the best way to input vector data.

• Common digitising errors:

• Omission: a feature is missed, so the data has gaps.
• Undershoot: a line stops short of the line it should meet. This leaves an open polygon or a broken network.

• Overshoot: a line goes past the line it should meet. This leaves small extra bits called "dangles".

• These errors are fixed in the data verification and editing step.

• Raster → vector (vectorisation): software traces the edges of grid cells into lines and polygons.
• It is done mainly to save storage.
• Auto-traced lines have a "stair-step" look with too many vertices (corner points), so they must be smoothed [5].

Strengths and weaknesses (NCERT Box 4.2)

• Advantages:
• Compact: uses less storage than raster.
• Precise map output: lines and edges look sharp, not stepped.
• Good for network analysis: for example, routes along roads or pipelines.

• Good for projection change (redrawing the map on a different map projection).

• Disadvantages:

• Complex data structure.
• Overlay is harder (overlay means laying one map layer on top of another to combine them).
• Does not fit satellite images. These are always raster.

Where it occurs

• Bhuvan geoportal (ISRO, run by NRSC, Hyderabad):
• Offers vector layers of administrative boundaries, roads and railways, panchayat boundaries, river basins and sub-basins, soils and census data [3].
• Vector data is served through GeoServer and GeoWebCache [4].

• Layers are shared as OGC-compliant WMS (Web Map Service, an international standard that lets any GIS software read the map) [4].

• SVAMITVA scheme (Survey of India):

• Over 2.8 lakh villages mapped with drones in Andhra Pradesh, Haryana and Karnataka (reported February 2025) [2].

• The drone images are raster. The property boundaries digitised from them are vector polygons [2].

• USGS geologic mapping (2002), United States:

• Geologic maps were scanned, cleaned and then auto-vectorised: software traced the pixels into lines [5].

• 32 maps of 7.5-minute quadrangles were joined into one 30 × 60-minute map [5].

• Everyday Indian uses: road and canal networks, cadastral plots (land-ownership parcels), and district and state boundaries in planning maps.

Don't confuse with

• Raster data model: stores space as a grid of equal cells (pixels), each holding one value. It suits continuous surfaces like elevation and rainfall. Vector stores coordinates and suits discrete features like roads.
• Attribute data: the descriptive tables (names, population, soil type). Vector data is only the location and shape part. The two are joined in the "linking" step.
• Rasterisation (vector → raster): turns vector into a grid. It is the more common conversion because most spatial analysis is raster-based. Vectorisation (raster → vector) is done mainly to save storage.
• Scanning: gives a raster image of a paper map, not vector. Vector data comes from digitisation or from vectorising the scan.

Prelims Hooks

• Vector stores features as points, lines and polygons from (x, y) or (x, y, z) coordinates. A road is a line; a district is a polygon.
• Topology (connectivity, adjacency, containment) belongs to the vector model. It is built after errors are corrected.
• Vector is better for network analysis and projection change. Raster is better for overlay and high spatial variability.
• Trap: "Vector is compatible with remote sensing images" is false. Satellite images are always raster.
• Omission, undershoot and overshoot are digitising errors. Digitisation is the best way to input vector data.
• On Bhuvan, vector data is served through GeoServer and GeoWebCache as OGC-compliant WMS [4].

Mains Points

• The choice of data model shapes planning (GS-I):
• Vector suits networks and boundaries such as roads, canals and cadastral plots. It supports route and network analysis.

• Raster suits flood extent from satellite images, DEMs and rainfall. Disaster mapping and Bhuvan's thematic services use both together [3].

• Accurate vector records support governance (GS-III):

• Drone-based SVAMITVA maps (2.8 lakh+ villages) give precise vector property polygons. Survey of India's CORS network supports them by giving exact positions [2].

• These records help land titles and loans, and they reduce disputes [2].

• Data quality and compatibility problems:

• Digitising errors break topology, so careful verification is essential.
• Departments use different scales, classes and datums, so vector layers often do not line up across district and state boundaries.
• NGP 2022 responds with a unified data interface, a redefined National Geodetic Framework and common standards [2].

Related concepts

• Raster data model
• Topology
• Digitisation
• Scanner
• Charge-coupled device
• Georeferencing
• Raster-vector conversion
• Exact matching
• Hierarchical matching
• Fuzzy matching

Read more

• Raster and vector data, data input and matching