initial re-implementation of the LDN-squared borough tile map from viz-tools

[jamesscottbrown]

What does this change?

Why?

How?

Related issues:

Does this introduce new dependencies?

How is it tested?

How is it documented?

Are light and dark themes considered?

Is it complete?

• [ ] Have you included changeset file?
• [ ] If this adds a new component, is it exported via index.js?

[ChrisKnightLDN]

this is known colloquially as LDN-squared to avoid confusion we should probably call it that where needed