Support for Cities inside a region/state/provinces.

Hi there,

Is there a way to drill countries' provinces/region/states to there respective cities.

### Example
- Used map-layer: ```canadaLow.js```
- Expected Feature:
``` Expand to Ontario (Which is available) -> then we have cities inside of it like Toronto etc. ```

- Current Feature:
``` Only Provinces can be drilled not cities. ```

Best Regards,
Mark