LINKThis has to do with temperature site quality. Some sites where temperatures are sampled are not very good...they have artificial heat sources or heat sinks (concrete, asphalt or high urban density) that make for warmer average temperatures. Some are judged to be very, very accurate because they don't have any of these interfering factors.
So...what do you do with this mix of data?
Well, apparently, if you are a warmist who is hell bent on manipulating data in an ever growing mission to enhance your funding you adjust the highly accurate sites to be more like the warmer highly inaccurate sites. And just like magic, your results are even higher than the average of the warmer highly inaccurate sites. Poof! Instant funding!