Measuring these is a problem since they lack clear boundaries.

As an unincorporated community, Mountain Green lacks official boundaries, so population estimates vary.

The horizons differ greatly in thickness and generally lack sharp boundaries.

But most terms in this general realm still lack clear boundaries.

They participated in what were described as "immoral games" together, lacking boundaries between emperor and subject.

As social classes lack distinct boundaries the average American may have a status in the area where the lower middle and working class overlap.

As social classes lack clear boundaries and overlap there are no definite income thresholds as for what is considered middle class.

It is centered close to the Galactic Center and lacks hard boundaries.

And as a shrink might say, they lack boundaries.

As such they are conceptual constructs, usually lacking distinct boundaries.