Allow users to selectively mark flooded areas

[arky]

At the moment when a user marks a street, the whole street selected as flooded. This might not accurately reflect the flood situation on the ground.

First report in down street codebase here: https://github.com/tailwindlabs/flood-map/issues/4

Current work-flow

User zoom in and tap/click to select a street
The whole street or road is highlighted as flooded.

I think it is important to let the users select the areas that currently are flooded selectively. They can select a street, highlight only those areas that are effected. Or they can draw polygon shapes to highlight open areas that are currently flooded.

Expected work-flow

User zoom in and tap/click to select a street
A part of the street is highlighted.
User can resize the highlighted to show which areas are affected.
Alternatively we can let users paint a large area using polycon fill to highlight areas underwater. The user can use resize markers or paint with touch gestures.

[planemad]

This is ideally how it should work, but a lot more challenging to implement. The simplicity of the codebase and the entire system is that it just uses the street data already loaded in the browser as vector tiles. This means all streets are broken up into a segment at the edge of a tile.

Moving away from this mechanism will require a lot more spatial analysis and data validation. Something to do while doing a code rewrite.