The SpatiaLite module for SQLite adds features for handling geographic and spatial data. For an example of what you can do with it, see the tutorial Building a location to time zone API with SpatiaLite, OpenStreetMap and Datasette.

To use it with Datasette, you need to install the mod_spatialite dynamic library. This can then be loaded into Datasette using the --load-extension command-line option.


Installing SpatiaLite on OS X

The easiest way to install SpatiaLite on OS X is to use Homebrew.

brew update
brew install spatialite-tools

This will install the spatialite command-line tool and the mod_spatialite dynamic library.

You can now run Datasette like so:

datasette --load-extension=/usr/local/lib/mod_spatialite.dylib

Installing SpatiaLite on Linux

SpatiaLite is packaged for most Linux distributions.

apt install spatialite-bin libsqlite3-mod-spatialite

Depending on your distribution, you should be able to run Datasette something like this:

datasette --load-extension=/usr/lib/x86_64-linux-gnu/

If you are unsure of the location of the module, try running locate mod_spatialite and see what comes back.

Building SpatiaLite from source

The packaged versions of SpatiaLite usually provide SpatiaLite 4.3.0a. For an example of how to build the most recent unstable version, 4.4.0-RC0 (which includes the powerful VirtualKNN module), take a look at the Datasette Dockerfile.

Spatial indexing latitude/longitude columns

Here’s a recipe for taking a table with existing latitude and longitude columns, adding a SpatiaLite POINT geometry column to that table, populating the new column and then populating a spatial index:

import sqlite3
conn = sqlite3.connect('museums.db')
# Lead the spatialite extension:
# Initialize spatial metadata for this database:
conn.execute('select InitSpatialMetadata(1)')
# Add a geometry column called point_geom to our museums table:
conn.execute("SELECT AddGeometryColumn('museums', 'point_geom', 4326, 'POINT', 2);")
# Now update that geometry column with the lat/lon points
    UPDATE events SET
    point_geom = GeomFromText('POINT('||"longitude"||' '||"latitude"||')',4326);
# Now add a spatial index to that column
conn.execute('select CreateSpatialIndex("museums", "point_geom");')
# If you don't commit your changes will not be persisted:

Making use of a spatial index

SpatiaLite spatial indexes are R*Trees. They allow you to run efficient bounding box queries using a sub-select, with a similar pattern to that used for Searches using custom SQL.

In the above example, the resulting index will be called idx_museums_point_geom. This takes the form of a SQLite virtual table. You can inspect its contents using the following query:

select * from idx_museums_point_geom limit 10;

Here’s a live example:

pkid xmin xmax ymin ymax
1 -8.601725578308105 -2.4930307865142822 4.162120819091797 10.74019718170166
2 -3.2607860565185547 1.27329421043396 4.539252281188965 11.174856185913086
3 32.997581481933594 47.98238754272461 3.3974475860595703 14.894054412841797
4 -8.66890811920166 11.997337341308594 18.9681453704834 37.296207427978516
5 36.43336486816406 43.300174713134766 12.354820251464844 18.070993423461914

You can now construct efficient bounding box queries that will make use of the index like this:

select * from museums where museums.rowid in (
    SELECT pkid FROM idx_museums_point_geom
    -- left-hand-edge of point > left-hand-edge of bbox (minx)
    where xmin > :bbox_minx
    -- right-hand-edge of point < right-hand-edge of bbox (maxx)
    and xmax < :bbox_maxx
    -- bottom-edge of point > bottom-edge of bbox (miny)
    and ymin > :bbox_miny
    -- top-edge of point < top-edge of bbox (maxy)
    and ymax < :bbox_maxy

Spatial indexes can be created against polygon columns as well as point columns, in which case they will represent the minimum bounding rectangle of that polygon. This is useful for accelerating within queries, as seen in the Timezones API example.

Importing shapefiles into SpatiaLite

The shapefile format is a common format for distributing geospatial data. You can use the spatialite command-line tool to create a new database table from a shapefile.

Try it now with the North America shapefile available from the University of North Carolina Global River Database project. Download the file and unzip it (this will create files called narivs.dbf, narivs.prj, narivs.shp and narivs.shx in the current directory), then run the following:

$ spatialite rivers-database.db
SpatiaLite version ..: 4.3.0a       Supported Extensions:
spatialite> .loadshp narivs rivers CP1252 23032
Loading shapefile at 'narivs' into SQLite table 'rivers'
Inserted 467973 rows into 'rivers' from SHAPEFILE

This will load the data from the narivs shapefile into a new database table called rivers.

Exit out of spatialite (using Ctrl+D) and run Datasette against your new database like this:

datasette rivers-database.db \

If you browse to http://localhost:8001/rivers-database/rivers you will see the new table… but the Geometry column will contain unreadable binary data (SpatiaLite uses a custom format based on WKB).

The easiest way to turn this into semi-readable data is to use the SpatiaLite AsGeoJSON function. Try the following using the SQL query interface at http://localhost:8001/rivers-database:

select *, AsGeoJSON(Geometry) from rivers limit 10;

This will give you back an additional column of GeoJSON. You can copy and paste GeoJSON from this column into the debugging tool at to visualize it on a map.

To see a more interesting example, try ordering the records with the longest geometry first. Since there are 467,000 rows in the table you will first need to increase the SQL time limit imposed by Datasette:

datasette rivers-database.db \
    --load-extension=/usr/local/lib/mod_spatialite.dylib \
    --config sql_time_limit_ms:10000

Now try the following query:

select *, AsGeoJSON(Geometry) from rivers
order by length(Geometry) desc limit 10;

Importing GeoJSON polygons using Shapely

Another common form of polygon data is the GeoJSON format. This can be imported into SpatiaLite directly, or by using the Shapely Python library.

Who’s On First is an excellent source of openly licensed GeoJSON polygons. Let’s import the geographical polygon for Wales. First, we can use the Who’s On First Spelunker tool to find the record for Wales:

That page includes a link to the GeoJSON record, which can be accessed here:

Here’s Python code to create a SQLite database, enable SpatiaLite, create a places table and then add a record for Wales:

import sqlite3
conn = sqlite3.connect('places.db')
# Enable SpatialLite extension
# Create the masic countries table
conn.execute('select InitSpatialMetadata(1)')
conn.execute('create table places (id integer primary key, name text);')
# Add a MULTIPOLYGON Geometry column
conn.execute("SELECT AddGeometryColumn('places', 'geom', 4326, 'MULTIPOLYGON', 2);")
# Add a spatial index against the new column
conn.execute("SELECT CreateSpatialIndex('places', 'geom');")
# Now populate the table
from shapely.geometry.multipolygon import MultiPolygon
from shapely.geometry import shape
import requests
geojson = requests.get('').json()
# Convert to "Well Known Text" format
wkt = shape(geojson['geometry']).wkt
# Insert and commit the record
conn.execute("INSERT INTO places (id, name, geom) VALUES(null, ?, GeomFromText(?, 4326))", (
   "Wales", wkt

Querying polygons using within()

The within() SQL function can be used to check if a point is within a geometry:

   within(GeomFromText('POINT(-3.1724366 51.4704448)'), places.geom);

The GeomFromText() function takes a string of well-known text. Note that the order used here is longitude then latitude.

To run that same within() query in a way that benefits from the spatial index, use the following:

    within(GeomFromText('POINT(-3.1724366 51.4704448)'), places.geom)
    and rowid in (
        SELECT pkid FROM idx_places_geom
        where xmin < -3.1724366
        and xmax > -3.1724366
        and ymin < 51.4704448
        and ymax > 51.4704448