Crunchy Spatial: Tile Serving

Paul Ramsey
PostgreSQL PostGIS spatial

Crunchy Spatial logo 2Beautiful, responsive maps are best built using vector tiles, and PostgreSQL with PostGIS can produce vector tiles on-the-fly.

However, to use vector tiles in a beautiful, responsive map, you need to be able to access those tiles over the HTTP web protocol, and you need to be able to request them using a standard XYZ tiled map URL.

Crunchy Spatial_Spatial Diagram-1

It's possible to write your own HTTP wrapper for the PostGIS vector tile generator, but you don't need to!

pg_tileserv is a lightweight vector tile server specifically written to publish tiles from a PostgreSQL/PostGIS database.

pg_tileserv has the following features:

  • Written in Go to allow for simple deployment of binaries with no complex dependency chains or library versioning issues.
  • Ready-to-run defaults so that basic deployment just requires setting a database configuration string and running the program.
  • Simple web user interface to explore the published tile services, and view the services as maps.
  • On-the-fly attribute filtering to strip out columns you don't want to retrieve from the server, for smaller, faster tiles.
  • Function-based tile generation, so you can generate tiles from any function that takes in XYZ tile coordinates and outputs MVT tiles.

public parcels

Want to see pg_tileserv in action? Here's a five-step demo! (Most of the steps just involve getting some spatial data in a database: if you already have a database, just skip down to step 3 and input your own database connection information).

  1. Make a database, and enable PostGIS.

    createdb postgisftw
    psql -d postgisftw -c 'create extension postgis'
  2. Download some spatial data, and load it into PostGIS.

    curl -L -o https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/50m/cultural/ne_50m_admin_0_countries.zip
    unzip ne_50m_admin_0_countries.zip
    shp2pgsql -s 4326 -D -I ne_50m_admin_0_countries | psql -d postgisftw
  3. Download and unzip the pg_tileserv binary for your platform

  4. Set the DATABASE_URL environment variable to point to your database, and start the service.

    export DATABASE_URL=postgresql://postgres@localhost:5432/postgisftw
    ./pg_tileserv --debug
  5. Point your browser to the service web interface URL.

  6. Explore the data!

The service includes both a human-viewable interface, and a JSON-based API for programmatic service discovery. The JSON API starting point is:

* http://localhost:7800/index.json

You can see examples of maps that configure using the JSON API by viewing the source of the human-viewable interface.

pg_tileservUsing the data loaded in this example, building a web map that visualizes the tiles is as simple as pointing to the tile source URL. A web map can be as small as these examples (Leaflet, Openlayers, Mapbox GL JS):

<html lang="en">
<head>
<meta charset="utf-8">
<title>Vector Tiles in Leaflet</title>

<!-- CSS for Leaflet map  -->
<link rel="stylesheet" href="https://unpkg.com/leaflet@1.5.1/dist/leaflet.css"
integrity="sha512-xwE/Az9zrjBIphAcBb3F6JVqxf46+CDLwfLMHloNu6KEQCAWi6HcDUbeOfBIptF7tcCzusKFjFw2yuvEpDL9wQ=="
crossorigin="" />

<!-- JS for Leaflet map  -->
<script src="https://unpkg.com/leaflet@1.5.1/dist/leaflet.js"
integrity="sha512-GffPMF3RvMeYyc1LWMHtK8EbPv0iNZ8/oTtHPx9/cc2ILxQ+u905qIwdpULaqDkyBKgOaB57QTMg7ztg8Jm2Og=="
crossorigin=""></script>

<!-- Leaflet plugin for vector tiles support -->
<script type="text/javascript"  src="https://unpkg.com/leaflet.vectorgrid@1.2.0"></script>

<!-- Set up a full-screen map -->
<style>
html, body, #map { height: 100%; width: 100%; }
body { padding: 0; margin: 0; }
#map { z-index: 1; }
</style>

</head>

<body>

<!-- Put the map in this element -->
<div id="map"></div>

<script>
// Leaflet map object
var map = L.map('map').setView([0, 0], 2);

// Add a base map layer to the map
var baseUrl = "https://maps.wikimedia.org/osm-intl/{z}/{x}/{y}.png";
var baseLayer = L.tileLayer(baseUrl).addTo(map);

// Add the tile layer to the map
// https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/50m/cultural/ne_50m_admin_0_countries.zip
var vectorServer = "http://localhost:7800/";
var vectorLayerId = "public.ne_50m_admin_0_countries";
var vectorUrl = vectorServer + vectorLayerId + "/{z}/{x}/{y}.pbf";
var vectorTileStyling = {};
// Rendering options
vectorTileStyling[vectorLayerId] = {
"fill": true,
"fillColor": "green",
"fillOpacity": 0.1,
"color": "green",
"opacity": 0.7,
"weight": 2
};
var vectorTileOptions = {
"rendererFactory": L.canvas.tile,
"vectorTileLayerStyles": vectorTileStyling
};
var vectorLayer = L.vectorGrid.protobuf(vectorUrl, vectorTileOptions).addTo(map);

</script>

</body>
</html>

leaflet tile map

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