[OSGeo-Standards] Irregular tile coverage in TMS?

[Mateusz Loskot]

Folks,

I'm reading the TMS spec which says:

"a coverage of regularly sized and spaced images that taken together
form a complete visual representation of the entire area of coverage"

I understand the size and spacing constraints.
What I'm missing, however, is what TMS says about "topological"
regularity of tiles within a coverage.

I attached basic drawing with two example tile coverages:

a) blue - regular coverage, rectangular

b) red - irregular coverage

Is only blue version kosher for TMS or both versions are valid?

Best regards,

-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org