In general, just a habit from Astropy, could you leave spaces between different sections of the method? For example

```
# Check that the input sites fall within the domain.
         for site in sites:
             for coord,limit in zip(site,domain):
                 if coord < limit[0] or coord > limit[1]:
                     raise ValueError('a site is outside the domain')

         # Store the domain.
         self._domain = deepcopy(domain)

        # Build the two tessellations.
```

(just for readability). Similarly, leave an empty line before new methods.