[joquarky]

Put simply, "the map is not the territory"

[kazinator]

It would be a bad convention for a map to use valleys to represent mountains.

[coldtea]

If that just a nominal change, such as just switching the color convention it uses for montains vs valleys, then it would be fine.

And that's the case with positive/negative.

[trelane]

Or, as Monty Python has rightly pointed out, "it's only a model."