Let us suppose two people, poring over a map spread on a table; make it an Ordnance Survey two-and-half-inch to the mile one. They are planning a cycle journey together that will traverse the area shown on the map, by one of several routes. Both are skilled in reading maps, so that in tracing a possible route they can visualise the terrain it would take them through, the steepness of the gradients, the possibility of views and so on.

For the time that they are studying the routes, they are wholly absorbed: there is just them and the map; they feel the need of nothing else. The map and their discussions are interwoven, interactive. At length they decide the best way to go.

But the journey, for whatever reason, is never made as they planned.

Only years later, one of them undertakes it, in remembrance of the other, who has died.

The relation between the first scene, with the map, and the second, illustrates what I mean to show by this Venn diagram:

And both are intended to show the relation between our everyday construct of the world (the blue bit, which by convention, we deem to be reality, and corresponds to the map scene) and how the world really is.