{"id": "spatialite:importing-geojson-polygons-using-shapely", "page": "spatialite", "ref": "importing-geojson-polygons-using-shapely", "title": "Importing GeoJSON polygons using Shapely", "content": "Another common form of polygon data is the GeoJSON format. This can be imported into SpatiaLite directly, or by using the Shapely Python library. \n 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: \n spelunker.whosonfirst.org/id/404227475 \n That page includes a link to the GeoJSON record, which can be accessed here: \n data.whosonfirst.org/404/227/475/404227475.geojson \n Here's Python code to create a SQLite database, enable SpatiaLite, create a places table and then add a record for Wales: \n import sqlite3\n\nconn = sqlite3.connect(\"places.db\")\n# Enable SpatialLite extension\nconn.enable_load_extension(True)\nconn.load_extension(\"/usr/local/lib/mod_spatialite.dylib\")\n# Create the masic countries table\nconn.execute(\"select InitSpatialMetadata(1)\")\nconn.execute(\n \"create table places (id integer primary key, name text);\"\n)\n# Add a MULTIPOLYGON Geometry column\nconn.execute(\n \"SELECT AddGeometryColumn('places', 'geom', 4326, 'MULTIPOLYGON', 2);\"\n)\n# Add a spatial index against the new column\nconn.execute(\"SELECT CreateSpatialIndex('places', 'geom');\")\n# Now populate the table\nfrom shapely.geometry.multipolygon import MultiPolygon\nfrom shapely.geometry import shape\nimport requests\n\ngeojson = requests.get(\n \"https://data.whosonfirst.org/404/227/475/404227475.geojson\"\n).json()\n# Convert to \"Well Known Text\" format\nwkt = shape(geojson[\"geometry\"]).wkt\n# Insert and commit the record\nconn.execute(\n \"INSERT INTO places (id, name, geom) VALUES(null, ?, GeomFromText(?, 4326))\",\n (\"Wales\", wkt),\n)\nconn.commit()", "breadcrumbs": "[\"SpatiaLite\"]", "references": "[{\"href\": \"https://pypi.org/project/Shapely/\", \"label\": \"Shapely\"}, {\"href\": \"https://whosonfirst.org/\", \"label\": \"Who's On First\"}, {\"href\": \"https://spelunker.whosonfirst.org/id/404227475/\", \"label\": \"spelunker.whosonfirst.org/id/404227475\"}, {\"href\": \"https://data.whosonfirst.org/404/227/475/404227475.geojson\", \"label\": \"data.whosonfirst.org/404/227/475/404227475.geojson\"}]"} {"id": "spatialite:making-use-of-a-spatial-index", "page": "spatialite", "ref": "making-use-of-a-spatial-index", "title": "Making use of a spatial index", "content": "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 . \n 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: \n select * from idx_museums_point_geom limit 10; \n Here's a live example: timezones-api.datasette.io/timezones/idx_timezones_Geometry \n \n \n \n \n \n \n \n \n \n \n pkid \n \n \n xmin \n \n \n xmax \n \n \n ymin \n \n \n ymax \n \n \n \n \n \n \n 1 \n \n \n -8.601725578308105 \n \n \n -2.4930307865142822 \n \n \n 4.162120819091797 \n \n \n 10.74019718170166 \n \n \n \n \n 2 \n \n \n -3.2607860565185547 \n \n \n 1.27329421043396 \n \n \n 4.539252281188965 \n \n \n 11.174856185913086 \n \n \n \n \n 3 \n \n \n 32.997581481933594 \n \n \n 47.98238754272461 \n \n \n 3.3974475860595703 \n \n \n 14.894054412841797 \n \n \n \n \n 4 \n \n \n -8.66890811920166 \n \n \n 11.997337341308594 \n \n \n 18.9681453704834 \n \n \n 37.296207427978516 \n \n \n \n \n 5 \n \n \n 36.43336486816406 \n \n \n 43.300174713134766 \n \n \n 12.354820251464844 \n \n \n 18.070993423461914 \n \n \n \n \n \n You can now construct efficient bounding box queries that will make use of the index like this: \n select * from museums where museums.rowid in (\n SELECT pkid FROM idx_museums_point_geom\n -- left-hand-edge of point > left-hand-edge of bbox (minx)\n where xmin > :bbox_minx\n -- right-hand-edge of point < right-hand-edge of bbox (maxx)\n and xmax < :bbox_maxx\n -- bottom-edge of point > bottom-edge of bbox (miny)\n and ymin > :bbox_miny\n -- top-edge of point < top-edge of bbox (maxy)\n and ymax < :bbox_maxy\n); \n 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.", "breadcrumbs": "[\"SpatiaLite\"]", "references": "[{\"href\": \"https://timezones-api.datasette.io/timezones/idx_timezones_Geometry\", \"label\": \"timezones-api.datasette.io/timezones/idx_timezones_Geometry\"}]"} {"id": "spatialite:spatialite-warning", "page": "spatialite", "ref": "spatialite-warning", "title": "Warning", "content": "The SpatiaLite extension adds a large number of additional SQL functions , some of which are not be safe for untrusted users to execute: they may cause the Datasette server to crash. \n You should not expose a SpatiaLite-enabled Datasette instance to the public internet without taking extra measures to secure it against potentially harmful SQL queries. \n The following steps are recommended: \n \n \n Disable arbitrary SQL queries by untrusted users. See Controlling the ability to execute arbitrary SQL for ways to do this. The easiest is to start Datasette with the datasette --setting default_allow_sql off option. \n \n \n Define Canned queries with the SQL queries that use SpatiaLite functions that you want people to be able to execute. \n \n \n The Datasette SpatiaLite tutorial includes detailed instructions for running SpatiaLite safely using these techniques", "breadcrumbs": "[\"SpatiaLite\"]", "references": "[{\"href\": \"https://www.gaia-gis.it/gaia-sins/spatialite-sql-5.0.1.html\", \"label\": \"a large number of additional SQL functions\"}, {\"href\": \"https://datasette.io/tutorials/spatialite\", \"label\": \"Datasette SpatiaLite tutorial\"}]"}