Say for example you have a Lunar mine with Titanium.
At 100% hotspot, you get $3 for the resources Gold, Lead, Coal & Oil that your nation has access to.
At 50% hotspot, you get $1.50 for the resources Gold, Lead, Coal & Oil that your nation has access to.
At 75% hotspot, you get $2.25 for the resources Gold, Lead, Coal & Oil that your nation has access to.
etc