A thermal map can clearly show that different urban surfaces heat up differently. But a red patch alone doesn’t tell us how a person feels there, or what should be done about it.

The surface is not the air

LST, or land surface temperature, describes the temperature of the surface observed by a sensor: a roof, the ground or the top of a tree canopy, for example. It is not the same quantity as the air temperature in a weather forecast. The distinction is explained in NASA’s overview of land surface temperature.

Before interpreting the map

First check what was measured, when the image was captured, what the legend means and how much ground each value represents.

Every image has a context

Comparing surfaces only makes sense when we know the time of capture and the conditions in which the data was collected. To understand change over time, we need comparable images and a consistent processing method.

Landsat surface-temperature products have documented limitations, including missing data and difficulties near clouds or over small features. These are reasons to interpret the data carefully, rather than dismiss it. USGS documents the limitations of Collection 2 Surface Temperature products.

A map helps us decide where to ask a question. The design needs an answer on the ground.

What this means for a garden

Applying this to design starts with relating a heat pattern to what is actually on site. A large paved area, the position of trees, shade from a building and how people use the space are all parts of the same task.

For a decision about a single tree or a narrow garden, we need to check whether the data’s spatial resolution fits the scale of the question. A map of the wider area cannot, on its own, tell us where to plant a tree or how large its planting pit should be.

From observation to decision

  • Identify a pattern using good-quality, comparable data.
  • Check local conditions, existing shade and how the space is used.
  • Consider soil, water, roots and room for the future canopy.
  • Design the intervention and decide how its development will be monitored.

The value of a satellite view goes beyond an impressive image. For a designer, it is useful when it helps us understand a place and make a better decision.

Connected scales