How Sundial works

Sundial shows where the sun and shadows fall on real buildings, for any address, on any day of the year.

What you can do

Find a place. Search an address or place name, paste coordinates, or use your device's location.
Pick a date and time. Drag the sliders, which snap to the equinoxes and solstices, sunrise, solar noon or sunset, or play through a day or a whole year. Shadows update as you go.
See the sun's path. The arc for the selected day is drawn over the map, next to the June and December solstice arcs and a compass.
Map hours of sun. The sun-hours view colours every patch of ground and roof by how many hours of direct sunlight it gets on the selected day. Hover or tap a spot to read its total.
Read the numbers. Sunrise, solar noon, sunset, day length, and the sun's height and bearing, all in the location's own time zone.
Share the view. The address bar always holds the place, date and time, so a copied link opens the same view.

How it's calculated

The sun's position comes from standard astronomical formulas (the SunCalc library) for the chosen coordinates and moment. Sundial lights a 3D model of the surrounding buildings from that direction and renders the shadows in your browser with WebGL. The sun-hours map repeats this every ten minutes from sunrise to sunset and adds up which surfaces were lit.

Where the data comes from

Buildings: Footprints and heights from OpenStreetMap contributors, served as vector tiles by OpenFreeMap (OpenMapTiles schema).
Trees: Individually mapped trees from OpenStreetMap, fetched through the Overpass API.
Ground map: Standard OpenStreetMap map tiles.
Search: Address search and place names from Photon by komoot, which is built on OpenStreetMap data.

Limits to keep in mind

Buildings load within 300 m of the chosen point. Taller buildings further away can still cast shadows that Sundial does not show.
The ground is treated as flat, so hills, slopes and terrain shading are not modelled.
Building heights are only as good as the map. Where OpenStreetMap has no height or number of floors, a typical height is assumed.
Only trees mapped individually in OpenStreetMap appear, drawn with a simple shape, and they are shown in full leaf all year.
Clouds, weather and reflections are not taken into account; the sun-hours map shows possible direct sun on a clear day.

Sundial is a planning aid and a curiosity, not a survey. For decisions that depend on exact sunlight, such as planning applications or buying a property, check on site or with a professional.

Requirements

Sundial runs in any current browser with JavaScript and WebGL, on desktop or mobile. Nothing is installed and there is no account to create.