A geographic information system (GIS) is software that stores and analyses anything with a location, such as roads, pipes, power lines, plots of land and customers, and answers questions by place. Governments, town planners, telecom operators and utilities use it most. Utilities are the companies that supply electricity, water and gas.
A GIS keeps data in layers, one layer for each kind of thing. A water department may have one layer for pipes, one for valves, one for roads and one for household connections. There are two kinds of layer. Vector layers hold points, lines and areas: a valve is a point, a pipe is a line and a plot of land is an area. Each one carries a record of facts, such as a pipe's diameter, material and year of laying. Raster layers hold images made of a grid of cells, such as satellite photographs or a map of ground height.
The power of a GIS is in questions that combine layers by place. Which houses lie within 500 metres of this school? Which plots does the new road cross? Which areas flooded last monsoon, and which of our power lines run through them? A GIS can also store a network, such as pipes that join at valves, and trace what is connected to what.
Say a water main bursts under a road in Nagpur at 7 a.m. An engineer in the city's water department marks the leak on the GIS map. Because the pipes are stored as a network, the GIS traces the valves that must be closed to cut off that stretch of pipe: four valves. It then lists every connection fed by that stretch: 2,300 households, a school and a clinic. The department sends an SMS to the households, and it sends a water tanker to the clinic. The repair crew's tablet shows exactly where the four valves are, because they are buried under the road and cannot be seen.
Most GIS work starts with a base map, such as a digital map of roads and buildings. New layers come from drone surveys and from satellite imagery analytics. Results often go on to other systems. An electricity company's grid control software takes its model of the network from the GIS. Network planning software for mobile towers and fibre is a GIS built for one industry.
India's government uses GIS at a national scale. The PM Gati Shakti National Master Plan puts the projects of many ministries, such as roads, railways, gas pipelines and power lines, on one shared GIS. So a department planning a new road can see where a pipeline is already planned.
A GIS differs from a digital map. A digital map is the shared picture of the world that everyone uses. A GIS is a tool in which an organisation places its own data on that picture and analyses it.