Big picture
Every phenomenon on Earth has a location: a school, a river, a road, a rainfall station. Spatial information technology deals with collecting, storing, analysing and displaying such location-based information using computers. Its core tool is the Geographic Information System (GIS).
GIS helps planners find the best site for a hospital, map flood-prone areas, track the spread of diseases, and manage traffic. This chapter explains what GIS is, its components, how spatial data are stored, and the kinds of analysis it allows.
Learning goals
Define spatial information technology and GIS.
Explain the advantages of GIS over manual methods.
Describe the components of GIS.
Distinguish spatial and attribute data, and raster and vector formats.
Explain the sequence of activities in GIS.
Explain overlay, buffer and network analysis.
Core ideas
1. Spatial information technology and GIS
Spatial information technology is the application of technology (computers, satellites, GPS) to collect, store, retrieve, display, manipulate, manage and analyse spatial information.
It combines remote sensing, the Global Positioning System (GPS), GIS, digital cartography and database management.
A Geographic Information System (GIS) is a system for capturing, storing, checking, integrating, manipulating, analysing and displaying data related to positions on the Earth's surface. It links where things are (location) with what they are (attributes).
2. Advantages of GIS over manual methods
Advantage | Explanation |
|---|---|
Interactive queries | Users can ask questions, such as "which villages lie within 5 km of a river?", and get answers instantly |
Integration of data | Spatial data from different sources (maps, satellite images, GPS, tables) can be combined |
Easy updating | Data can be edited and updated quickly; maps can be redrawn instantly |
Spatial analysis | Overlay, buffer and network analysis that are slow or impossible manually |
Flexible output | Maps at any scale and in different forms, along with tables and charts |
Linking to non-spatial data | Attribute information (population, land use) is linked to locations |
3. Components of GIS
Component | Role |
|---|---|
Hardware | Computers, digitisers, scanners, printers, plotters and storage devices |
Software | Programs to input, store, analyse and display spatial data (such as QGIS or ArcGIS) |
Data | The most important and costly component: spatial (location) and attribute (non-spatial) data |
People | Skilled users who design, manage and interpret GIS |
Procedures | The methods and rules followed to produce accurate results |
4. Spatial and attribute data
Spatial data describe location and shape: points (wells, towns), lines (roads, rivers) and polygons (districts, lakes).
Attribute (non-spatial) data describe the characteristics of spatial features, such as a town's population, a road's width or a district's literacy rate. They are stored in tables linked to the spatial features.
5. Spatial data formats: raster and vector
Feature | Raster format | Vector format |
|---|---|---|
Structure | A grid of cells (pixels), each with a value | Points, lines and polygons defined by coordinates |
Example sources | Satellite images, aerial photographs, scanned maps | Digitised maps, GPS data |
Best for | Continuous data such as elevation, temperature, land cover | Discrete features such as roads, boundaries, wells |
Data volume | Large | Compact |
Appearance | Can look blocky (pixelated) when zoomed | Smooth, accurate lines and boundaries |
Analysis | Overlay analysis is simple and fast | Network analysis and topology are efficient |
6. Sequence of activities in GIS
Spatial data input: data are entered from existing maps (by digitisation or scanning), satellite images, aerial photographs, GPS surveys and field data.
Entering attribute data: attribute data are typed or imported and linked to spatial features through a common identifier.
Data verification and editing: errors such as missing lines, gaps or wrong labels are found and corrected; topology (spatial relationships) is built.
Spatial analysis: queries, overlay, buffer and network analysis are carried out.
Output: results are shown as maps, tables, graphs and reports.
7. Spatial analysis
Analysis | Meaning | Example |
|---|---|---|
Overlay analysis | Superimposing two or more layers to find areas that meet several conditions | Overlaying land use, soil and slope layers to find land suitable for farming; overlaying old and new land-use maps to see changes |
Buffer analysis | Creating a zone of a specified distance around a point, line or polygon | Finding all villages within 2 km of a highway; identifying areas within 500 m of a river that may flood |
Network analysis | Analysing connected networks such as roads and pipelines | Finding the shortest route between two places, best location for a fire station, or tracing the flow of water in pipes |
8. Data sources: GPS and remote sensing
GPS (Global Positioning System) uses signals from satellites to give the precise location (latitude and longitude) of a receiver on Earth. It is used in surveying, navigation and data collection.
Remote sensing collects information about the Earth's surface using sensors on satellites or aircraft, without physical contact. Satellite images (raster data) are a major input for GIS. India's IRS satellites and the NRSC in Hyderabad provide such data.
9. Applications
Urban planning: locating schools and hospitals, managing utilities and traffic.
Disaster management: mapping flood, earthquake or landslide-prone areas.
Agriculture and environment: crop monitoring, forest mapping, watershed management.
Health: mapping disease spread.
Business: finding sites for shops based on population and transport.
A reliable approach to questions
Define GIS and list its five components.
Distinguish spatial and attribute data with examples.
Compare raster and vector formats in a table.
List the five steps of GIS activities in order.
Match each type of analysis (overlay, buffer, network) to an example.
Connections that matter
India: transport and communication describes India's remote sensing satellites.
Graphical representation explains thematic maps that GIS can produce.
Computer Science: databases explains how attribute tables are stored and queried.
Common mistakes
Calling attribute data spatial data. Attribute data describe characteristics, not location.
Saying satellite images are vector data. They are raster data (grids of pixels).
Confusing buffer analysis (zones around features) with overlay analysis (superimposing layers).
Leaving out people and procedures as GIS components.
Revision checklist
I can define spatial information technology and GIS.
I can explain the advantages and components of GIS.
I can distinguish spatial and attribute data, and raster and vector formats.
I can list the sequence of GIS activities.
I can explain overlay, buffer and network analysis with examples.