Mapping the World with GIS: Digital Maps That Think

Imagine you are a city planner for London. A new hospital needs to be built — but where? You need to think about where the most people live, which areas have no hospital nearby, and whether the site floods in heavy rain. Each of those facts is a different kind of information about the same city. How could you look at all of them at once on a single map? That is exactly the problem GIS was invented to solve. Before we dive in, try to answer the warm-up question below.

GIS stands for Geographic Information System. It is a computer-based tool that stores, analyses, and displays information linked to specific locations on Earth. Unlike a paper map — which shows a fixed picture — a GIS map can hold many separate layers of data and let you switch them on and off, compare them, and run calculations. Think of a GIS map like a stack of transparent plastic sheets, each one the same size and aligned to the same area of the world. On one sheet you might draw every river. On the next, every road. On the next, every school. On the next, the population density (how many people live per square kilometre). When you stack all the sheets and look down through them, you see everything at once. You can also remove sheets to focus on just one topic. Each sheet in GIS is called a LAYER. Layers can hold two types of data: • Vector data — points, lines, or polygons (shapes). A hospital is a point; a road is a line; a country's border is a polygon. • Raster data — a grid of tiny squares (pixels), each holding a value. Satellite images and temperature maps use raster data. GIS software — such as ArcGIS or the free tool QGIS — can do more than just display layers. It can ask spatial questions: Which schools are within 1 km of a flood zone? Which neighbourhoods have no green space within 500 m? That kind of analysis is called a spatial query. A GIS MAPPING PROJECT follows a clear process: 1. Ask a geographic question (e.g. 'Where in Nairobi are children most at risk from air pollution?'). 2. Collect and add data layers relevant to that question (e.g. air quality readings, school locations, traffic density, wind direction). 3. Analyse the layers — look for overlaps, patterns, or gaps. 4. Interpret your findings and draw a conclusion linked to your question. 5. Present the map with a title, legend, scale bar, and north arrow — the four features every good map needs. Real GIS projects are used by governments, charities, scientists, and businesses every day. The UN uses GIS to track refugee movements. Ecologists use it to map deforestation in the Amazon. Transport planners in Tokyo use it to model where new metro lines should go.