Buffer analysis

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

Meaning

Buffer analysis (also called buffering or proximity analysis) means drawing a zone of a fixed distance around a map feature, such as a point, a line or an area, to find out who or what lies inside that zone. It is one of the four spatial analysis operations listed in NCERT. It answers one simple question, "who is near this?", which is why it is used to find people a service reaches and people a hazard puts at risk.

Explanation

What it is and why GIS can do it

• GIS (Geographic Information System): a computer system that links data about places on Earth and shows it as a map [6].
• GIS uses two kinds of data together:
• Spatial data: where a thing is and what shape it has. For example, a hospital is a point and a road is a line.

• Attribute data: facts about the thing, such as number of beds, road type or population.

• An ordinary database only stores records. A GIS can also ask "how near?" Buffer analysis is one of the tools that does this.

• NCERT's four spatial analysis operations: 1. Overlay analysis 2. Buffer analysis 3. Network analysis 4. Digital Terrain Model (DTM / DEM)

How it works: step by step

• Step 1: Define the problem. For example: "Which villages have no hospital within 10 km?"
• Step 2: Pick the feature. Mark the hospitals as points on the map.
• Step 3: Set the distance and draw the zone. Draw rings of the chosen distance (for example 2 to 10 km) around each feature.
• Step 4: Lay the zones over other data. Place the rings on top of settlement and population layers.
• Result:
• Places inside a ring are served (or exposed to a hazard).
• Places outside every ring are underserved (they have no service nearby). New facilities can be planned there.

Types: buffers around the three vector features

• Vector data store features as points, lines and polygons (areas). A buffer can be drawn around all three:

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

Conditions and limits

• It measures straight-line distance only. This is distance "as the crow flies". It ignores roads, rivers and hills.
• A village 5 km away across a river with no bridge falls inside a 5 km buffer.
• But people there may not actually be able to reach the hospital.

• Network analysis fixes this by measuring real distance along roads.

• It often works together with overlay. In landfill siting (choosing a site for a garbage dump), buffers are drawn first:

• A safe distance around water bodies, so groundwater and rivers stay clean.
• A safe distance around settlements, for health reasons and because of the smell.

• These buffered layers are then overlaid with land use or slope. Only the land that passes every test is left as a suitable site.

• Good base maps give better buffers. The more exact the map, the more exact the zone.

Where it occurs

• NCERT case: hospitals in western Uttar Pradesh (Fig. 4.12, 4.13)
• Districts, from north to south: Saharanpur → Muzaffarnagar → Meerut → Ghaziabad → Gautam Buddh Nagar → Aligarh.

• Rings of 2 to 10 km were drawn around hospitals. Places outside all rings showed where health care was lacking.

• Bhuvan Municipal GIS, Ludhiana (Punjab):

• Bhuvan is a web portal run by NRSC (National Remote Sensing Centre) under ISRO. It has a buffer analysis tool that 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].

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

• PM GatiShakti National Master Plan: launched on 13 October 2021 and developed by BISAG-N (Bhaskaracharya National Institute for Space Applications and Geo-informatics). This GIS platform stacks 1,614+ data layers from 44 central ministries and 36 states/UTs [3][4]. Buffers mark clearance zones when roads, railways and pipelines are planned together [3].
• Environmental belts: corridors along rivers and coasts, and belts around parks (eco-sensitive zones).
• Software: ArcView / ArcGIS (by Esri) and GeoMedia are commercial. QGIS is free and open-source. All of them are used around the world to draw buffers.

Don't confuse with

• Network analysis (service area): a buffer uses straight-line distance. A network service area uses real distance or time along connected roads, such as an ambulance's 15-minute zone.
• Overlay analysis: overlay stacks two or more thematic layers (maps of one theme each, such as soil or land use) of the same area to make a new layer, for example Aligarh land use in 1974 vs 2001. A buffer needs only one feature and a distance, and it gives a zone or ring.
• Buffer zone of a biosphere reserve: this is an area on the ground set aside for conservation, placed around the protected core. It is a land-management zone, not a GIS operation.
• Digital Terrain Model (DTM / DEM): a digital 3-D model of land height. It shows relief (the rise and fall of the land), not nearness to a feature.

Prelims Hooks

• Buffer analysis is also called proximity analysis. Buffers can be drawn around points, lines and areas (polygons). A point gives a ring, a line gives a corridor, and an area gives a belt.
• NCERT's buffer example: 2–10 km rings around hospitals in Saharanpur, Muzaffarnagar, Meerut, Ghaziabad, Gautam Buddh Nagar and Aligarh, all in western Uttar Pradesh. Do not mix it up with the overlay example, which is Aligarh land use, 1974 vs 2001.
• NCERT's four spatial analysis operations are overlay, buffer, network analysis and DTM. Trap: "classification" and "geo-referencing" are not on this list.
• A buffer measures straight-line distance. Real travel distance along roads comes from network analysis, which suits vector data, not raster.
• The Bhuvan Municipal GIS buffer tool was shown with Ludhiana (Punjab) [2].
• Exam pairing: population served or affected → buffer. Urban change detection → overlay. Best route → network.

Mains Points

• Health-care equity (GS-I/II): buffer analysis finds underserved areas.
• In the western UP hospital case, villages outside the 2–10 km rings show where health care is lacking.
• New hospitals can then be placed where they reach the most people.

• Network service areas make this more exact by measuring real road travel, not straight-line distance.

• Disaster and environment (GS-III): buffers mark risk zones and protection zones.

• 1 km exposure zones around chemical units, and corridors along rivers and coasts, support NDMA-style risk planning.
• Buffers around water bodies and settlements, combined with overlay, help find safe landfill sites.

• The National Geospatial Policy 2022 aims for 5–10 cm mapping in urban and rural areas and a national DEM by 2030. These will make buffers more exact [5].

• Infrastructure planning (GS-III): PM GatiShakti uses buffers (clearance zones) together with overlay (to avoid forests and settlements) and network analysis (to plan routes that join different modes of transport) at national scale. This cuts delays and duplicated work across ministries [3].

Related concepts

• Spatial analysis
• Overlay analysis
• Sieve mapping
• Network analysis

Read more

• Spatial analysis: overlay, buffer and network