Satellite data is wonderful for regional work, but when you need to see individual buildings, roads, or field boundaries, you need aerial imagery. Orthophotos, aerial photographs corrected so every pixel sits in its true map position, can reach resolutions of 10 to 25 centimetres, a hundred times sharper than Sentinel-2. Much of it is free, if you know where to look.

Your first stop should always be the national mapping agency or open-data portal of the country you are mapping. Many governments now publish orthophotos openly: the USGS NAIP program covers the United States at 60 centimetre to 1 metre resolution on a regular cycle, several European countries publish national orthophotos through their geoportals, and many others release imagery through open-data initiatives. These sources are authoritative, documented, and usually the highest quality available for that country.

Check the licence and the date before downloading. Some national datasets are fully open, others are free for non-commercial use only, and a few require attribution in a specific form. Note the capture year too: a five-year-old orthophoto can mislead badly in a fast-growing suburb, where whole neighbourhoods may be missing.

High-resolution aerial imagery raises a responsibility that satellite data rarely does: it can show people, vehicles, and private property in recognisable detail. Before publishing a map built on drone or low-altitude imagery, consider whether individuals are identifiable and whether the licence permits your intended use. Blurring or aggregating sensitive detail is a small step that prevents real harm, and it is increasingly expected of professional mapmakers.

Currency is the other responsibility. Aerial imagery goes out of date faster than satellite imagery because it captures a moment in such detail: a new building, a removed tree, or a changed road layout can make a two-year-old orthophoto misleading. Always state the capture date on the map or in its metadata, and warn readers when the imagery predates known changes. A map that hides its imagery date invites readers to trust it more than they should.