Went out before the moon came up and got some readings in different areas nearby. The idea was to verify whether the map showing light levels is correct or accurate. In addition, to check the calibration of the SQM-L meter versus the iPhone app.
The lower point (6.1 Bortle) is just into an Indian reservation. These readings were taken between 9:00-9:30PM, 25 degrees C.
The upper point (5.8 Bortle) is on the other side of some mountains nearby; I think to the north of this location is another reservation. Readings taken between 10:00-10:30 PM.
The readings at the middle point are my backyard, between 10:30-10:45. The moon rose shortly after.
Conclusions
1) The map’s darker areas are in fact measurably slightly darker. The 6.1 site in particular was noticeably darker.
2) My area just has too many neighbors with outside lights on!
3) The iPhone app clearly has much more variability than the SQM-L. Perhaps if I take about 10-15 readings and average things work out OK. It also looks like I need to add about .15 to the iPhone value, although this difference changes with the different reading values; a greater difference is shown at the 6.1 value than the 5.65.