When the real-time map is zoomed-out in a region with many sensors, a few of the sensors are displayed and the rest are dropped. Often, the sensors displayed are not representative of the air quality in that region.
For instance, I sometimes see one anomalously high AQI in a region that otherwise has low AQI. Perhaps that sensor is detecting smoke from someone’s backyard barbecue, or the sensor is broken. When the map is zoomed-in, all the sensors are shown and it is obvious that the high reading is an outlier. But when the map is zoomed-out, the sensor with high AQI often persists while most of the other sensor readings are dropped. This is very misleading.
Perhaps when there are too many sensors to display in a region, the map might display an average of sensor readings in that region, rather than choosing a single sensor to display. Alternatively, it might discard outliers and display one sensor that is most representative of the nearby sensors.