datasette-leaflet-freedraw 0.3.1
Draw polygons on maps in Datasette
License: Apache License, Version 2.0
Requires Python: >=3.6

# datasette-leaflet-freedraw

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Draw polygons on maps in Datasette

Project background: [Drawing shapes on a map to query a SpatiaLite database](https://simonwillison.net/2021/Jan/24/drawing-shapes-spatialite/).

## Installation

Install this plugin in the same environment as Datasette.

    $ datasette install datasette-leaflet-freedraw

## Usage

If a table has a SpatiaLite `geometry` column, the plugin will add a map interface to the table page allowing users to draw a shape on the map to find rows with a geometry that intersects that shape.

The plugin can also work with arbitrary SQL queries. There it looks for input fields with a name of `freedraw` or that ends in `_freedraw` and replaces them with a map interface.

The map interface uses the [FreeDraw](https://freedraw.herokuapp.com/) Leaflet plugin.

## Demo

You can try out this plugin to run searches against the GreenInfo Network California Protected Areas Database. Here's [an example query](https://calands.datasettes.com/calands?sql=select%0D%0A++AsGeoJSON%28geometry%29%2C+*%0D%0Afrom%0D%0A++CPAD_2020a_SuperUnits%0D%0Awhere%0D%0A++PARK_NAME+like+%27%25mini%25%27+and%0D%0A++Intersects%28GeomFromGeoJSON%28%3Afreedraw%29%2C+geometry%29+%3D+1%0D%0A++and+CPAD_2020a_SuperUnits.rowid+in+%28%0D%0A++++select%0D%0A++++++rowid%0D%0A++++from%0D%0A++++++SpatialIndex%0D%0A++++where%0D%0A++++++f_table_name+%3D+%27CPAD_2020a_SuperUnits%27%0D%0A++++++and+search_frame+%3D+GeomFromGeoJSON%28%3Afreedraw%29%0D%0A++%29&freedraw=%7B%22type%22%3A%22MultiPolygon%22%2C%22coordinates%22%3A%5B%5B%5B%5B-122.42202758789064%2C37.82280243352759%5D%2C%5B-122.39868164062501%2C37.823887203271454%5D%2C%5B-122.38220214843751%2C37.81846319511331%5D%2C%5B-122.35061645507814%2C37.77071473849611%5D%2C%5B-122.34924316406251%2C37.74465712069939%5D%2C%5B-122.37258911132814%2C37.703380457832374%5D%2C%5B-122.39044189453125%2C37.690340943717715%5D%2C%5B-122.41241455078126%2C37.680559803205135%5D%2C%5B-122.44262695312501%2C37.67295135774715%5D%2C%5B-122.47283935546876%2C37.67295135774715%5D%2C%5B-122.52502441406251%2C37.68382032669382%5D%2C%5B-122.53463745117189%2C37.6892542140253%5D%2C%5B-122.54699707031251%2C37.690340943717715%5D%2C%5B-122.55798339843751%2C37.72945260537781%5D%2C%5B-122.54287719726564%2C37.77831314799672%5D%2C%5B-122.49893188476564%2C37.81303878836991%5D%2C%5B-122.46185302734376%2C37.82822612280363%5D%2C%5B-122.42889404296876%2C37.82822612280363%5D%2C%5B-122.42202758789064%2C37.82280243352759%5D%5D%5D%5D%7D) showing mini parks in San Francisco:

```sql
select
  AsGeoJSON(geometry), *
from
  CPAD_2020a_SuperUnits
where
  PARK_NAME like '%mini%' and
  Intersects(GeomFromGeoJSON(:freedraw), geometry) = 1
  and CPAD_2020a_SuperUnits.rowid in (
    select
      rowid
    from
      SpatialIndex
    where
      f_table_name = 'CPAD_2020a_SuperUnits'
      and search_frame = GeomFromGeoJSON(:freedraw)
  )
```

![Screenshot of the plugin in action](https://static.simonwillison.net/static/2021/datasette-leaflet-freedraw.png)

## Development

To set up this plugin locally, first checkout the code. Then create a new virtual environment:

    cd datasette-leaflet-freedraw
    python3 -mvenv venv
    source venv/bin/activate

Or if you are using `pipenv`:

    pipenv shell

Now install the dependencies and tests:

    pip install -e '.[test]'

To run the tests:

    pytest