Final answer:
The variations in altimeter settings between weather reporting points are primarily caused by unequal heating of the Earth's surface.
Step-by-step explanation:
The variations in altimeter settings between weather reporting points are primarily caused by unequal heating of the Earth's surface. When a specific area heats up more than its surroundings, the air in that area expands, creating a high pressure area. Conversely, when an area cools more than its surroundings, the air in that area contracts, creating a low pressure area. These pressure differences lead to variations in altimeter settings between weather reporting points.