What determines the quantity of MU (Mind Units) gained by a field?

When we make a fields with 3 portals in Ingress, it captures some MU (Mind Units) that will be credited to the faction count.

How is determined the quantity of MU captured, is it based :

• on the surface covered ?
• on the population density ?
• on the quantity of XM covered ?

Solution 1:

Mind Units (MU) are how the global faction scores are tallied. MU are calculated based off estimations of humans within control fields.

In my experience, MU is calculated as the field surface size times population density in the area. I've built several fields over industrial zone with very low human population and it resulted in same MU score as building a similar field over a densely populated areas in the same city.

And it looks like population density information is aggregated on a very high level.