Spatial analysis

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

Meaning

Spatial analysis (also called geographic analysis) is the set of GIS (Geographic Information System) tasks that use spatial data (where a thing is) and attribute data (what the thing is) together to answer real questions about places and to model trends. NCERT lists four of these operations: overlay, buffer, network analysis and the digital terrain model.

It matters because spatial analysis is what sets a GIS apart from other information systems. An ordinary database only stores records. A GIS can also ask "where?", "how near?" and "what overlaps what?". Planners use these answers to decide where to put hospitals, roads, landfills and new towns.

Explanation

How it works: problem → analysis → answer

• Two kinds of data are used together:
• Spatial data: the location and shape of a thing. For example, a hospital is a point, a road is a line and a district is an area.

• Attribute data: the details of that thing. For example, the number of beds, the type of road or the population.

• The sequence:

• First, define the problem. For example: "Which villages have no hospital within 10 km?"
• Then, run the analysis on spatial and attribute data together.

• Result: answers and trend models that decision-makers can use.

• NCERT's four operations: 1. Overlay analysis 2. Buffer analysis 3. Network analysis 4. Digital Terrain Model (DTM / DEM): a digital 3-D model of land height.

• India's base height data: CartoDEM v3 (a DEM made from Cartosat satellite images) is on Bhuvan for India and nearby countries: Bangladesh, Bhutan, Nepal, Pakistan and Afghanistan [2].

Overlay analysis: the hallmark of GIS

• Overlay analysis: placing two or more thematic layers of the same area on top of each other to make a new layer (NCERT Fig. 4.7).
• Thematic layer: a map of just one theme, such as soil, land use, roads or water bodies.

• The new layer shows where the themes meet or match.

• It is called the hallmark (defining feature) of GIS because few other systems can do it. Britannica describes overlay as GIS's ability to put new information on top of existing data and show it in colour on screen. It is used for decisions in geology, ecology, land use, demographics and transport [6].

• Sieve mapping is the older, manual form of overlay:
• Each theme was traced on a transparent sheet.
• The sheets were stacked on a light table (a glass table lit from below).
• Light passed only through the unshaded parts. These were the areas that met every condition.

• GIS overlay is the digital form of sieve mapping. It is faster and exact, and it can be run again with new data.

• Change detection: comparing the same area at two dates by overlaying the two maps.

• Land-suitability analysis, for example finding a site for a landfill (a garbage dumping site):
• Layer A: water bodies, plus a safe distance around them, are removed. This keeps groundwater and rivers clean.
• Layer B: settlements, plus a safe distance around them, are removed for health reasons and to keep the smell away.
• Layer C: another condition, such as land use or slope.
• Overlay the layers → only land that passes every condition is left. These are the suitable sites.
• Here buffers are drawn first and then overlaid, so the two operations work together.

Buffer analysis: proximity analysis

• Buffer analysis: drawing a zone of a set distance around a feature to find who or what lies inside it. It is also called proximity analysis (analysis of nearness).
• Buffers can be drawn around all three vector feature types:

Feature type	Example	Buffer shape	Use
Point	Hospital, well, factory	Circle or ring	Population served or exposed
Line	Road, river, railway	Corridor (strip) along the line	River-bank protection zone, impact of road widening
Area (polygon)	Lake, forest, city	Belt around the edge	Eco-sensitive zone around a park

• Exposure zone: households within 1 km of a chemical unit are marked as being at risk from leaks or pollution. This helps with disaster planning.

Network analysis

• Network analysis: studying movement along connected lines. A network is made of links (roads, tracks) and nodes (junctions, stations).
• What it finds:
• Shortest route: the least distance between two places.
• Fastest route: the least travel time, after allowing for speed limits and traffic.

• Service area: all places that can be reached within a set time or distance, such as an ambulance's 15-minute zone.

• Networks studied: roads, railways, pipelines (oil, gas, water) and rivers (river flow and inland waterways).

• Why vector data suit it best:
• Vector data store features as points, lines and polygons. A road is then one connected line with a direction and a length.
• Raster data store the world as a grid of cells. This breaks a line into separate squares and loses the links between them.

Operation	Basic question	Input	Output	NCERT / Indian example
Overlay	What is where, together? What changed?	2+ thematic layers of the same area	New combined layer	Aligarh land use, 1974 vs 2001
Buffer	Who is near this?	A point, line or area, plus a distance	Zone or ring	2–10 km rings around hospitals, western UP
Network	How do I get there? How far can I reach?	Connected line network (vector)	Route or service area	Road, rail and pipeline routing

Where it occurs

• Aligarh, western Uttar Pradesh (NCERT overlay case): Aligarh lies in the Ganga–Yamuna Doab (the land between the Ganga and Yamuna rivers).
• Layer 1: urban land use in 1974. Layer 2: urban land use in 2001.
• The overlay shows land that changed use, such as farmland that became built-up area.

• Result: a map of land transformation and urban sprawl (a city spreading outward, without a plan, onto nearby farmland and open land) (Fig. 4.8–4.10).

• Western Uttar Pradesh hospitals (NCERT buffer case): the districts, from north to south, are Saharanpur → Muzaffarnagar → Meerut → Ghaziabad → Gautam Buddh Nagar → Aligarh.

• Hospitals are marked as points, and rings of 2 to 10 km are drawn around each one (Fig. 4.12, 4.13).

• The rings are overlaid on settlements and population. Places outside every ring are underserved (they lack nearby health care), so new hospitals can be planned there.

• Ludhiana, Punjab: NRSC's Bhuvan has a Municipal GIS buffer analysis tool. It finds amenities such as schools, hospitals and ATMs within a distance the user chooses. It was shown with the Ludhiana Municipal Corporation GIS. Bhuvan also offers proximity analysis to find nearby places [2].

• All of India: PM GatiShakti National Master Plan (NMP):
• It was launched on 13 October 2021. It is a GIS platform that stacks data layers of infrastructure, geographic features and demography (population data) for joint infrastructure planning [3][4].
• It was developed by BISAG-N (Bhaskaracharya National Institute for Space Applications and Geo-informatics) [3].
• It covers 44 central ministries and 36 states/UTs, with 1,614+ data layers (PIB, June 2025) [3].
• A Network Planning Group (NPG) examines project proposals. It is made up of the heads of network-planning divisions of the infrastructure ministries [3].

• Planning for roads, railways, gas pipelines and waterways is now done jointly on this platform [3].

• Software named in NCERT: ArcView / ArcGIS (commercial, by Esri), GeoMedia (commercial) and QGIS (free and open-source). The Indian web platform is Bhuvan (NRSC/ISRO) [2].

• Policy setting: National Geospatial Policy, 2022:
• It was notified on 28 December 2022 and replaced the National Map Policy, 2005. Its vision runs up to 2035 [5].
• Its targets for 2030 are mapping at 5–10 cm resolution for urban and rural areas, 50–100 cm for forests and wastelands, and a high-accuracy DEM for the whole country [5].
• Finer base maps make overlays and buffers more exact.

Don't confuse with

• Buffer vs network service area: a buffer measures straight-line ("as the crow flies") distance. A network service area measures real distance along roads. A village 5 km away across a river with no bridge falls inside a 5 km buffer, but it may be outside the network service area.
• Overlay analysis vs sieve mapping: both stack layers to find areas that meet every condition. Sieve mapping is the old manual method with tracings on a light table. Overlay is its digital form in a GIS.
• Spatial analysis vs an ordinary database: a database stores and sorts attribute records only. Spatial analysis joins those records to location, so it can answer "where" and "how near" questions.
• Spatial analysis operations vs data preparation steps: "classification" and "geo-referencing" are not among NCERT's four spatial analysis operations. Those four are overlay, buffer, network analysis and the DTM.

Prelims Hooks

• NCERT's four spatial analysis operations are overlay, buffer, network analysis and the digital terrain model. Trap: classification and geo-referencing are not on the list.
• Overlay analysis is the hallmark of GIS and the digital form of sieve mapping. NCERT's example is Aligarh urban land use, 1974 vs 2001, which shows urban sprawl.
• Buffer analysis is also called proximity analysis. NCERT draws 2–10 km rings around hospitals in Saharanpur, Muzaffarnagar, Meerut, Ghaziabad, Gautam Buddh Nagar and Aligarh, all in western UP.
• Network analysis suits vector data, not raster. QGIS is free and open-source, while ArcGIS and GeoMedia are commercial.
• The PM GatiShakti NMP was developed by BISAG-N. It has 1,614+ data layers and was launched on 13 October 2021 [3][4].
• The National Geospatial Policy 2022 replaced the National Map Policy 2005 and has a vision to 2035 [5]. The Bhuvan Municipal GIS buffer tool was shown with Ludhiana (Punjab) [2].

Mains Points

• Health-care equity and urban sprawl (GS-I):
• In the western UP hospital case, buffer analysis shows that villages outside the 2–10 km rings lack health care. Network service areas make this more exact because they measure real travel along roads.

• Overlaying Aligarh's 1974 and 2001 land-use maps shows farmland lost to built-up area. This helps with master plans, green belts and protecting farmland, and the method can be repeated for any fast-growing Indian city using Bhuvan and IRS images.

• Infrastructure planning (GS-III): PM GatiShakti stacks 1,614+ layers from 44 ministries and 36 states/UTs. It uses all three operations at national scale [3]:

• Overlay, to avoid forests and settlements.
• Buffer, to mark clearance zones.
• Network analysis, to plan multimodal routes (routes that use several transport modes).

• The result is fewer delays and less duplicated work [3].

• Disaster and environment (GS-III):

• Buffers around chemical units (1 km exposure zones), rivers and coasts support NDMA-style risk planning. So do overlays for choosing landfill sites.
• The National Geospatial Policy 2022 targets 5–10 cm mapping and a national DEM by 2030. These will make such analyses more exact [5].

Related concepts

• Overlay analysis
• Sieve mapping
• Buffer analysis
• Network analysis

Read more

• Spatial analysis: overlay, buffer and network