What is GIS?
A geographic information system (GIS) is computer software that stores, analyzes and displays data linked to locations. If a piece of data has a location, whether an address, coordinates or a boundary, it can go into a GIS.
GIS lets us ask spatial questions:
- Where is the best place for a new hospital?
- Which homes are at risk of flooding?
- How has a forest changed over 30 years?
- Where are disease cases clustering?
A Canadian, Roger Tomlinson, developed the first computerized GIS in the 1960s for the Canada Land Inventory. He is often called the "father of GIS."
How GIS works: layers
A GIS organizes data in layers, like transparent sheets stacked on top of each other.
| Layer | Example |
|---|---|
| Base map | satellite image or terrain |
| Roads | highways and streets |
| Water | rivers, lakes, floodplains |
| Land use | residential, commercial, farms, parks |
| Population | census data by neighbourhood |
| Points of interest | schools, hospitals, fire stations |
By combining layers, analysts find relationships. For example, overlay floodplains with homes and population to see who’s at risk.
Types of data
- Vector data uses points (a school), lines (a road) and polygons (a park or province). It’s good for features with clear boundaries.
- Raster data uses a grid of cells, like pixels in an image. Each cell holds a value, such as elevation, temperature or land cover. Satellite images are raster data.
Each feature can have attributes: information stored in a table, such as a school’s name, enrolment and grades.
Where the data comes from
- GPS (Global Positioning System): satellites let devices find precise locations. Other systems include Europe’s Galileo and Russia’s GLONASS.
- Remote sensing: satellites, aircraft and drones collect images and measurements from a distance. Examples include NASA’s Landsat program (since 1972) and Canada’s RADARSAT satellites, which can see through clouds and darkness.
- Surveys and censuses, such as Statistics Canada data.
- Crowdsourcing: platforms like OpenStreetMap, built by volunteers.
- Sensors: traffic counters, weather stations and phones.
Spatial analysis techniques
Spatial analysis finds patterns and relationships based on location.
| Technique | What it does | Example |
|---|---|---|
| Buffer | creates a zone around a feature | all homes within 500 m of a highway |
| Overlay | combines layers | farmland that is also in a floodplain |
| Proximity / network analysis | finds nearest or fastest routes | fastest ambulance route |
| Hot spot analysis | finds statistically significant clusters | crime or disease clusters |
| Change detection | compares images over time | glacier retreat, urban sprawl |
| Suitability analysis | ranks locations using several criteria | best site for a wind farm |
GIS in the real world
- Emergency management: mapping wildfire spread and evacuation routes
- Public health: tracking outbreaks, such as John Snow’s famous 1854 map of cholera cases in London, an early example of spatial analysis
- Urban planning: zoning, transit routes, housing
- Environment: habitat mapping, deforestation and climate monitoring
- Business: choosing store locations, delivery routes
- Indigenous land use: many First Nations use GIS to map traditional territories, place names and land use for land claims, stewardship and cultural preservation
Thinking critically about maps and data
- Data quality: Is the data accurate, current and complete?
- Scale and boundaries: results can change depending on how areas are drawn (the modifiable areal unit problem).
- Privacy: location data from phones can reveal sensitive information.
- Representation: maps can make choices about what to show and hide, shaping how people see a place.
- Access: who has the tools, skills and data to make maps?
Try it yourself
- Use a free tool, such as Google Earth or an online GIS viewer, to explore your community’s layers.
- Plan a buffer analysis: which schools are within 1 km of a busy highway?
- Compare satellite images of a place from different years and describe the changes.
- Design a suitability analysis for a new park: list your criteria and data layers.
Quick recap
- GIS stores, analyzes and displays location-based data in layers.
- Vector data uses points, lines and polygons; raster data uses grid cells.
- Data comes from GPS, remote sensing, surveys and crowdsourcing.
- Spatial analysis includes buffers, overlays, routing and hot spot analysis.
- GIS supports planning, emergency response, health and environmental work, but must be used critically.