Spatial data: where is it?
The location and shape of a feature, stored as coordinates. For example, the outline of a land parcel or the line of a pipeline.
GIS guide
What is GIS?
GIS stands for Geographic Information System. It is the technology behind maps that can answer questions: it stores information about places, layers it together, and shows patterns you would never see in a spreadsheet.
The basics
A map that knows what is on it.
A paper map shows you where things are. A GIS also knows what those things are, and it can calculate with them. Every feature on the map, such as a road, a building or a field, is linked to a record of facts about it.
That link is what makes GIS useful. You can ask which homes lie within 500 metres of a river, which sites are close to a main road and outside a flood zone, or how a coastline has moved in ten years, and get the answer as a map.
Attribute data: what is it?
The facts about that feature, stored in a table. For example, the parcel's owner type, land use, area and value.
The five parts of every GIS
- 1
Hardware
Computers, servers and field devices such as GNSS receivers, drones and tablets.
- 2
Software
Desktop GIS, spatial databases and web mapping tools that store, analyse and display data.
- 3
Data
Maps, satellite images, survey points and business records. The most valuable part of any GIS.
- 4
People
Analysts, surveyors and developers who build the system, and the teams who use its answers.
- 5
Methods
The rules and workflows that keep the data accurate and the results repeatable.
Two ways to store the world
Vector data
Points, lines and polygons with exact edges. Best for things with clear boundaries: wells, roads, buildings and land parcels.
Raster data
A grid of cells, each holding one value. Best for things that change gradually: satellite images, elevation, temperature and rainfall.
How layers work
One place, many layers of information.
A GIS stacks separate themes on top of each other, all lined up to the same coordinates. Compare them and you start to see cause and effect.
Imagery
Satellite and aerial photographs that show the ground as it really looks.
Land use
What each area is used for: homes, farms, industry, parks or forest.
Elevation
The height of the ground, used to study slopes, drainage and flood risk.
Soil
Soil types and properties that guide farming and construction.
Water
Rivers, lakes, drainage and groundwater, and how they connect.
Vegetation
Plant cover and crop health, often measured from satellite data.
Uses today
GIS is working behind the technology you use every day.
Any service that depends on location is likely to rely on GIS. These are some of the most common uses.
Smart cities
Planning zones, tracking building permits and deciding where new schools, parks and services are needed.
Navigation & transport
Live traffic, route planning and the road networks behind maps, ride-hailing and connected vehicles.
Farming
Reading crop health from satellites and drones, so water and fertiliser go only where they are needed.
Disasters & climate
Tracking storms, mapping floods and fires, and planning evacuation routes and relief.
Logistics & delivery
Optimising routes, tracking fleets and choosing where to place warehouses.
Utilities & energy
Mapping power, water and telecom networks, and finding good sites for solar and wind.
Public health
Mapping disease outbreaks and finding communities that are too far from a clinic.
Retail & business
Choosing store locations, defining sales territories and understanding where customers are.
Remote sensing
Studying the Earth without touching it.
Remote sensing means collecting information about the ground from a distance, using sensors on satellites, aircraft and drones. It is one of the biggest sources of data for GIS.
Most sensors record sunlight reflected from the surface, including wavelengths our eyes cannot see. Healthy plants, dry soil and clear water each reflect light differently, so these images can reveal things a normal photo cannot.
From satellite data to machine learning
- 1
Capture
Satellites, aircraft and drones collect images of the area of interest.
- 2
Prepare
Images are corrected for the atmosphere and terrain, and tied to real-world coordinates.
- 3
Measure
Spectral bands are combined into indices such as NDVI to measure vegetation, water and more.
- 4
Classify
Machine learning models are trained to sort each pixel into land cover classes such as forest, water or urban.
- 5
Compare
Images from different dates are compared to detect change over time.
- 6
Deliver
Results join other GIS layers as maps, dashboards and reports that support decisions.
20 key terms
Remote sensing terms, in plain language.
The words you will meet most often when working with satellite and aerial imagery.
1Remote sensing
Gathering information about something without physically touching it.
2Electromagnetic spectrum
The full range of radiation, from gamma rays to radio waves, ordered by wavelength.
3Wavelength
The distance between two neighbouring crests of a wave, written as lambda (λ).
4Sensor
The instrument that detects and records energy reflected or emitted from a surface.
5Platform
The vehicle that carries the sensor, such as a satellite, aircraft or drone.
6Passive remote sensing
Uses natural energy, mainly sunlight, reflected or emitted by the ground. Optical satellites work this way.
7Active remote sensing
Sends out its own signal and measures what returns, so it can work at night. Radar and LiDAR are examples.
8Spatial resolution
The size of ground each pixel covers. Smaller pixels show finer detail.
9Spectral resolution
How finely a sensor separates wavelengths. More, narrower bands can tell materials apart better.
10Radiometric resolution
How small a difference in energy a sensor can detect. Higher values capture subtler shades.
11Temporal resolution
How often a sensor revisits and images the same place.
12Pixel
The smallest element of a digital image, holding one value for each band.
13Swath width
The width of the strip of ground imaged in one pass of the sensor.
14False colour composite
An image that displays wavelengths in unnatural colours to make features stand out, such as healthy plants in red.
15NDVI
Normalised Difference Vegetation Index: (NIR − Red) ÷ (NIR + Red). It runs from −1 to +1, and higher values mean denser, healthier plants.
16Image classification
Assigning each pixel to a category of land cover or land use.
17Georeferencing
Giving an image real-world coordinates so it lines up with other map data.
18Orthorectification
Removing distortion caused by terrain, relief and sensor tilt, so distances on the image are true.
19DEM
Digital Elevation Model: a raster map of the height of the Earth's surface.
20Change detection
Comparing images of the same place from different dates to find what has changed.
Geoprocessing tools
Nine tools that answer most spatial questions.
Geoprocessing means running operations on map layers to create new information. These nine vector tools come up in almost every GIS project.
ToolWhat it doesGood for
Buffer
Draws a zone of a set distance around points, lines or polygons.
Finding schools within 1 km of a road, or mapping noise and environmental impact zones.
Clip
Cuts a layer to the shape of another polygon, like a cookie cutter.
Keeping only the roads inside a city boundary or study area.
Intersect
Keeps only the areas that overlap in all input layers, with attributes from each.
Finding where zoning meets flood zones, or habitats crossed by infrastructure.
Union
Combines polygon layers, keeping all areas and attributes from both.
Overlaying administrative boundaries with ecological zones for land management.
Erase
Removes the parts of a layer that overlap another layer.
Taking protected areas out of development zones, or water out of land use maps.
Merge
Joins several datasets of the same geometry type into one layer.
Combining road networks from different districts into a single file.
Dissolve
Removes inner boundaries by combining features that share a value.
Turning districts into provinces, or simplifying boundaries for analysis.
Spatial join
Copies attributes from one layer to another based on their location.
Adding population figures to points, or finding each customer's nearest branch.
Select by location
Selects features based on their spatial relationship with another layer.
Finding buildings inside flood zones, or farms within 500 m of a river.
Ground control points
How drone maps become accurate.
A ground control point, or GCP, is a marked spot on the ground whose exact coordinates have been measured with survey equipment such as a GNSS receiver or total station.
The targets are visible in the drone's photos, so the processing software can tie the images to their true position. This corrects errors in the drone's own positioning and camera geometry, and makes the final maps and 3D models far more reliable. Targets are usually high-contrast, black and white, flat, stable and easy to see from the air.
The workflow
- 1
Plan
Choose target locations across the site before the flight.
- 2
Survey
Measure each target accurately with RTK or PPK GNSS, or a total station.
- 3
Fly
Capture overlapping images, making sure the targets are clearly visible.
- 4
Process
Load the images and coordinates into photogrammetry software and mark each target.
- 5
Deliver
Produce accurate orthomosaics, elevation models and 3D models.
Good distribution
Targets spread evenly across the corners, edges and centre hold the whole model in place. More well-placed points generally mean better accuracy.
Poor distribution
Targets bunched together, or only along one edge, leave the rest of the site unsupported, so errors grow with distance.
Best practices
- Use high-contrast targets and keep them clean
- Spread targets evenly: corners, edges and centre
- Check each target is visible in several images
- Measure with survey-grade equipment
- Keep some points aside as independent checkpoints
- Label every point and its coordinates carefully
Common coordinate systems
- Geographic
- Latitude, longitude and height. Used worldwide, in degrees.
- Projected
- Flat map coordinates in metres, such as UTM. Good for measuring distance and area.
- Local
- A grid set up for one site, often used on construction projects.
Use the same coordinate system for your targets, images and final outputs.
Put GIS to work
Talk to our GIS teamHave a location question to answer?
From field survey to web maps, our GIS team can help you turn location data into decisions.