What Is an Online Shadow Map and How Do You Check Sunlight and Shade for a Place?

Updated

An online shadow map is a browser-based tool that simulates where shadows fall at a given place and time by modeling the sun's position against terrain, buildings, and trees. ShadeMap (shademap.app) is one example: it renders shadows for any date and time on Earth and runs in the browser, so you don't need to install or buy Google Earth Pro. Use it when you want to know whether a garden, balcony, house, or photo location will be in sun or shade at a specific moment — or across a whole day or season.

How an Online Shadow Map Works

The tool combines two inputs:

  • Sun position — calculated from the date, time, and the location's coordinates. This gives the sun's altitude (how high it is) and azimuth (which direction it comes from).
  • Surface geometry — the shape of the ground, plus the height and footprint of buildings and trees.

Where the sun's rays are blocked by that geometry, the tool draws a shadow. Because both inputs change, the same spot can be sunny at noon and shaded an hour later, or sunny in June and shaded in December.

ShadeMap's stated scope is broad: "Every mountain, building and tree shadow in the world simulated for any date and time." In practice, the accuracy of any shadow map depends on how current and detailed the underlying building and tree data is for your area, so treat results as a close guide rather than a survey.

How to Check Sunlight and Shade for a Place

  1. Open the tool in a browser. ShadeMap requires JavaScript to be enabled — if the page loads but nothing renders, that's the usual cause.
  2. Navigate to your location. Search or pan the map to the house, garden, or viewpoint you care about.
  3. Set the date and time. Move to the moment you're interested in — a specific morning, the summer solstice, or a date you're planning an event.
  4. Read the shadow layer. Shaded areas appear dark; sunlit areas stay clear. This tells you whether your spot is in sun or shade at that instant.
  5. Scrub through the day. Step the time forward to watch shadows sweep across the site. This is how you find the sunniest window or confirm when shade arrives.
  6. Repeat for other dates. Compare a winter date against a summer one to see how much sun exposure changes across the year.

What to look for

  • Sun position and sun path — where the sun rises, peaks, and sets relative to your location.
  • Sun exposure — the total sunlit time a spot receives on a given day.
  • Obstructions — which nearby building, tree, or hill is casting the shadow, and at what time.

Simulating Shadows from Buildings, Trees, and Terrain in 3D

Because the simulation is 3D, it accounts for height, not just footprint. A tall building casts a longer shadow than a low one at the same sun angle, and a tree's canopy shades differently from its trunk. Terrain matters too: a hill to the south can block low winter sun even when nothing is built there.

This is what separates a shadow map from a simple "is it north-facing?" rule of thumb. Two gardens on the same street can have very different sun exposure if one sits behind a taller neighbor.

Shadow Accumulation and Shadow Accrual Maps

ShadeMap notes it can generate shadow accumulation and shadow accrual maps. These go beyond a single moment:

  • Shadow accumulation shows how much shade builds up over a period — useful for seeing which parts of a garden stay shaded through the day.
  • Shadow accrual tracks shade over time in a similar cumulative way.

For planning, this is more useful than a single snapshot. If you're deciding where to put raised beds or a seating area, you want to know the total sun a spot gets across the growing season, not just at 2 p.m. on one day.

Practical Uses

  • Planning a garden or balcony — find the sunniest spots for sun-loving plants and the shadiest for shade-tolerant ones.
  • Sunrise and sunset photography — check when and where light will hit a subject before you travel.
  • Shadow studies and solar analysis — assess how a new structure or existing trees affect light on a site.
  • Home and property checks — see how much direct sun a room, yard, or patio receives at different times of year.

Limits to Keep in Mind

  • Data currency. Building and tree data can lag reality; a new extension or a felled tree won't appear until the data updates.
  • JavaScript required. The app won't run without it.
  • It's a simulation, not a measurement. Use it to plan and compare, then verify on site if the decision is important.

If you just need a quick answer — "will this spot be sunny at 4 p.m. in October?" — a shadow map gives it in a few clicks, with no software to install.