Predictive vs measured heatmaps
A predictive WiFi heatmap estimates coverage from a floor plan before anything is installed. An on-site survey measures the signal that is actually there. They answer different questions, and professional deployments use both.
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Predictive heatmaps
A predictive tool takes a floor plan, the wall materials, and the model and position of each access point, and calculates the expected signal everywhere using a propagation model. Each wall type subtracts an assumed loss: a few dB for drywall, much more for brick or concrete.
Prediction is the right tool when:
- The building is not finished or the network is not installed yet.
- You need to decide how many access points to buy and where to run cables.
- The site is large or demanding: several floors, warehouses, hospitals, lecture halls with hundreds of devices.
Its weakness is that it is only as good as its assumptions. A wall drawn as drywall that is really brick, a metal shelf, a neighbor's network on the same channel, an access point mounted somewhere other than planned: none of it shows up in the prediction.
On-site (measured) surveys
A survey measures signal strength at many points while you walk the site. The result shows the real network, including everything the model could not know about. There are two kinds:
- Passive surveys record the signal strength the device receives. This is what a measured heatmap shows.
- Active surveys also connect and test throughput, latency or packet loss.
The weakness of measuring is that it needs an existing network and someone on site, and it only covers the spots you actually measured. Between readings, the map is interpolated.
Side by side
| Predictive | Measured | |
|---|---|---|
| When | Before installation | After installation, or to diagnose an existing network |
| You need | Scaled plan, wall materials, access point models | A plan of any quality and a device that reads signal strength |
| Shows | What the design should achieve | What the network actually does |
| Misses | Wrong assumptions, furniture, interference, installation mistakes | Places you did not measure; networks that do not exist yet |
| Typical tools | Professional planning software, usually paid | Survey apps, from free tools to professional kits |
How professionals combine them
On a larger project the usual order is: predictive design, then installation, then a validation survey to check that the real network matches the design. The survey also catches what the design got wrong, and the fixes are checked with another survey.
Which one you need
For a home or a small office where the network already exists, measuring is usually enough and gives the more honest answer. You already have the router; the question is where its signal falls short, and whether moving it or adding a node fixes that. Measure, change one thing, measure again.
If you are planning a new building, many access points or a demanding environment, start with a predictive tool and validate with a survey afterwards.
Where WiFi Heatmapper fits
WiFi Heatmapper makes measured heatmaps: you take readings on site and it draws the map from them. It does not do predictive planning, so it cannot estimate coverage for a network that does not exist yet. It works well for the measuring half: diagnosing an existing network, checking a change, and the validation survey after an installation.
To try it, follow How to make a WiFi heatmap. For placing access points with measurements, see the small office guide.