Wi-Fi heat maps: calibration, coverage and site validation
A predictive Wi-Fi heat map estimates how a radio signal may behave across a drawing. It helps compare access point positions before installation. A coloured drawing does not establish measured coverage, user capacity or roaming performance.
Calibrate before placing access points
Import a clear plan and calibrate its scale against a known dimension. Check the crop and usable floor area. In the browser studio, walls and their losses are manually defined: PDF and DXF imports provide a drawing background, not automatic identification of wall construction.
An incorrectly calibrated plan changes radio distances and cable estimates together. If a 20 m corridor is accidentally entered as 10 m, the model will treat its endpoints as much closer than they really are. Correct the drawing scale before tuning transmitter power or adding more access points.
Worked example: interpreting an assumed loss budget
For teaching, assume transmit power is 18 dBm, net antenna contribution is 0 dB and the modelled path loss to a point is 75 dB. Received level is approximately 18 + 0 − 75 = −57 dBm. If a manually assigned wall adds another 10 dB loss, it becomes −67 dBm.
The 10 dB wall loss is a hypothetical input, not a rating for every concrete wall. Construction, frequency, doors, furnishings and mounting conditions affect actual attenuation. Use realistic radio settings and wall assumptions for the selected equipment and site.
Signal strength and interference are different checks
If received signal is −67 dBm and noise is −92 dBm, the signal-to-noise ratio is 25 dB. That is a training arithmetic example, not a universal acceptance threshold. Same-channel interference can reduce usable performance even where signal strength looks strong. The studio's SINR view depends on its modelled transmitters and noise assumptions; it does not measure neighbouring networks.
What the browser edition does not establish
- The rectangular auto-placement area does not automatically exclude external space or recognise room-specific requirements.
- Omnidirectional predictions do not reproduce every antenna pattern or mounting orientation.
- Coverage does not by itself prove client capacity, application throughput or roaming.
- Estimated cable distances still need routing and installation allowances.
After installation, carry out a site validation survey with representative clients and applications. Compare measured coverage, interference, throughput and roaming against the design requirements, then adjust the installation. Keep the survey evidence with the final access point layout and channel plan.
Further reference
Cisco: WLAN site survey guidelines. External guidance supports the topic; the illustrative inputs and worked examples above are prepared for this guide and are not manufacturer product selections.
Verify assumptions and results before project use. These worked examples are educational and do not provide authority approval. Report a correction.