Some of the Oxford dictionaries have
heat map, as a two-word compound, but no
heatmap. Wiktionary has the single-word format as an alternate form, and also as a verb, meaning "to create a heat map". Other dictionaries have neither variant.
The term, in both forms, is certainly in use. I'm not sure that the image you use is a good example of a heatmap, RTT. It's generally defined as a diagram using different colours to represent varying data values. here's an example, from the
Wikipedia article on the subject:
This example literally displays heat, but it could be any variable: average income, populations density, etc.
Use of the word heatmap is not confined to specialist writings. For example, on 31 May, in the
Yorkshire Evening Post:
Environet has launched its own interactive heatmap designed to inform homeowners and homebuyers of the local presence of knotweed and the potential risk to their property.
The word is occasionally used as a verb, as in this quote from Associated Press in 2021:
PatientBond has heatmapped the entire United States down to the block level according to the five psychographic segments, so we can be very precise in helping healthcare providers engage their communities with the appropriate messaging.
I'll add
heatmap,
heatmapping and
heatmapped, all as rare words.
