Building Interactive Maps

with PHP and JavaScript

Bonjour !


Alex Rock

Freelance PHP/Symfony dev & training consultant

Why a map?

A medieval world with horrific and gothic overtones

A table-top role-playing game

4 music albums

A board game (the Black Rose)

And more to come...

Shadows of Esteren

The genesis of a "map" application

What IS a map?

What IS a map?

What IS a map?


What IS a map?


What IS a map?


What IS a map?



Marker: {x,y}


Route: [ {x, y}, {x₁, y₁} ]




Zone: [ {x, y}, {x, y}, {x, y} ]



 ○ MarkerType


 ○ RouteType




 ○ ZoneType





     ○ TransportSpeedModifier
         ○ TransportType



"start" marker

"end" marker

Existing map providers


Baidu Maps ; Bing Maps ; Bhuvan ; Google Maps ; HERE WeGo ; Map World ; Mappy ; MapQuest ; Qwant Maps ; ViaMichelin ; WikiMapia ; etc.

Public domain

OpenStreetMap ; OpenSeaMap



These are all for the Earth... 😭

Okay, let's find a way to create a CUSTOM IMAGINARY map.

Tools to build maps

Backend renderer:

  • Osmarender: Converts OSM file into SVG with an XML stylesheet
  • Mapnik: Very advanced solution using PostGIS with tons of features
  • + A web-application to publish it online
  • + Maybe other tools I have not heard about...

Data Provider:

Well... Any database, but maybe PostgreSQL + PostGIS is the best for this purpose

Front-end renderer:

  • LeafletJS is the best option!

Tools that I used

Backend renderer:

  • PHP/Symfony web application
  • ImageMagick to create map tiles from an image
  • Entities and database managed with Doctrine
  • Frontend assets compiled with Gulp.js

Data Provider:

  • A simple MySQL database

Front-end renderer:

  • LeafletJS is the best option!
    Did you read the previous slide? 😉



The previously indicated tools are not the best options


(except Leaflet which is awesome)

Please use Mapnik + PostgreSQL + PostGIS + Leaflet.

Don't hurt yourself like I did.

Advantages to this stack

  • Symfony is good for programming
  • The web part is straightforward
  • I struggled learnt about relations & perfs with MySQL
  • Well, LeafletJS 🍃
  • I learnt ImageMagick ✨, graph theory, map & coordinate science...
  • Reimplemented Dijkstra algorithm in PHP
  • MySQL has support for geographical data, but I didn't know that back then.
  • Doctrine has no native support for geographical types. Some extensions exist, but they use PostGIS.
  • Implementing Dijkstra algorithm in PHP has a cost in terms of performances.
  • Since it's PHP, I had to find a proper way to send all data to Leaflet for front-end rendering. It also has a cost.

Disdvantages to this stack

Technical details

Shortest path problem

Shortest path problem

Shortest path problem

Shortest path problem

  • Dijkstra, most known, works with non-negative weights, lots of implementations.
  • Bellman–Ford, can handle negative weights.
  • A*, most known for games, can handle huge graphs.
  • Floyd–Warshall's algorithm, Johnson's algorithm, Viterbi algorithm...

Solving algorithms:

Shortest path problem

A* algorithm

Shortest path problem

Dijkstra's algorithm

Let's pick this one!

Calculate coordinates

Map coordinates system & projection

Map coordinates system & projection

Map coordinates system & projection

Most famous: Mercator projection

Map coordinates system & projection

Solution for us:


In a 10×10 2D space:


x = 0 → left

x = 10 → right


y = 0 → top

y = 10 → bottom

Frontend rendering

with LeafletJS



Awesome docs!

Easy to set up

// Matches a #map selector
var containerId = 'map';

var map =;

// This is for OpenStreetMap's default map layer
// Add a marker on the map
var marker = L.marker([51.5, -0.09]).addTo(mymap);
// Add a polygon on the map
var polygon = L.polygon([[51.509, -0.08], [51.503, -0.06],[51.51, -0.047]]).addTo(mymap);
// Add a multipoint line on the map
var polyline = L.polyline([[51.509, -0.08], [51.51, -0.047]]).addTo(mymap);

Map coordinates system & projection

By default, Leaflet uses Spherical Mercator projection, and uses mathematical rules to calculate distances & coordinates

L.CRS.EPSG3857 = Util.extend({}, Earth, {
    code: 'EPSG:3857',
    projection: SphericalMercator,
    transformation: (function() {
        var scale = 0.5 / (Math.PI * SphericalMercator.R);
        return toTransformation(scale, 0.5, -scale, 0.5);
export var SphericalMercator = {

    R: 6378137,
    MAX_LATITUDE: 85.0511287798,

    project: function(latlng) {
        var d = Math.PI / 180,
            max = this.MAX_LATITUDE,
            lat = Math.max(Math.min(max,, -max),
            sin = Math.sin(lat * d);

        return new Point(
            this.R * latlng.lng * d,
            this.R * Math.log((1 + sin) / (1 - sin)) / 2);

    unproject: function(point) {
        var d = 180 / Math.PI;

        return new LatLng(
            (2 * Math.atan(Math.exp(point.y / this.R)) - (Math.PI / 2)) * d,
            point.x * d / this.R);

    bounds: (function() {
        var d = 6378137 * Math.PI;
        return new Bounds([-d, -d], [d, d]);

Map coordinates system & projection

Simplify all the things!

L.CRS.XY = L.Util.extend({}, L.CRS.Simple, {
    code: 'XY',
    projection: L.Projection.LonLat,
    transformation: new L.Transformation(1, 0, 1, 0)

This tells LeafletJS to calculate coordinates on an [x,y] simple 2D system

But that's not finished...

Map coordinates system & projection

By default, LonLat projection (classic 2D) is still similar to Mercator in a point:

y = 0 is bottom

y = 10 is top

Let's reverse this!

L.LatLngBounds.prototype.extend = function (obj) {
    if (!obj) { return this; }

    var latLng = L.latLng(obj);
    if (latLng !== null) {
        obj = latLng;
    } else {
        obj = L.latLngBounds(obj);

    if (obj instanceof L.LatLng) {
        if (!this._southWest && !this._northEast) {
            this._southWest = new L.LatLng(, obj.lng);
            this._northEast = new L.LatLng(, obj.lng);
        } else {
            // Here we set "max" instead of "min" in the original code
   = Math.max(,;
            this._southWest.lng = Math.min(obj.lng, this._southWest.lng);

            // Here we set "min" instead of "max" in the original code
   = Math.min(,;
            this._northEast.lng = Math.max(obj.lng, this._northEast.lng);
    } else if (obj instanceof L.LatLngBounds) {
    return this;

Only the 2 lines after each comment  are custom.

The rest is copy/pasted from Leaflet.

Backend & data source

Old diagram

New diagram

Creating image tiles

Original map is 5433×4252 pixels wide.


I opted for 5 zoom levels.

With Leaflet, it's interpreted like this:

  • Zoom level 1 = "farthest" (tiny map)
  • Zoom level 5 = "closer" (original map size)

The higher the zoom, the more details you want on your map.

Determine zoom levels

zoom ratio = \frac{100}{2^{max-current}}

Equation to get the ratio for a given level:

  1. 6.25 %
  2. 12.5 %
  3. 25 %
  4. 50 %
  5. 100 %

Ratios for 5 zoom levels:

Determine zoom levels

Determine zoom levels

ImageMagick commands:

magick convert original_map.jpg
    -background "#000000" -extent "5433x5433" -resize "3.125%" -crop 168x168
    -background "#000000" -extent "168x168" -thumbnail "168x168" "output/$MAP_ID/0.jpg"

magick convert original_map.jpg
    -background "#000000" -extent "5433x5433" -resize "6.25%" -crop 168x168
    -background "#000000" -extent "168x168" -thumbnail "168x168" "output/$MAP_ID/1.jpg"

magick convert original_map.jpg
    -background "#000000" -extent "5433x5433" -resize "12.5%" -crop 168x168
    -background "#000000" -extent "168x168" -thumbnail "168x168" "output/$MAP_ID/2.jpg"

magick convert original_map.jpg
    -background "#000000" -extent "5433x5433" -resize "25%" -crop 168x168
    -background "#000000" -extent "168x168" -thumbnail "168x168" "output/$MAP_ID/3.jpg"

magick convert original_map.jpg
    -background "#000000" -extent "5433x5433" -resize "50%" -crop 168x168
    -background "#000000" -extent "168x168" -thumbnail "168x168" "output/$MAP_ID/4.jpg"

magick convert original_map.jpg
    -background "#000000" -extent "5433x5433" -resize "100%" -crop 168x168
    -background "#000000" -extent "168x168" -thumbnail "168x168" "output/$MAP_ID/5.jpg"


ImageMagick options "-extent", "-resize", "-thumbnail" and "-crop" need a "geometry" argument.


I made a regex for that:


(and an additionnal validator for non-regex-related checks)

Determine zoom levels

$ tree maps_tiles/$MAP_ID/
75 directories, 1498 files


ImageMagick output needs some sorting/renaming to be integrated in LeafletJS as a map tile layer.


And after that:

Manage all of that data

Want a glimpse of the rendering?

Search for elements in the map

Calculate a direction

Merci !