Éric Lemoine

A response to Iván's "Leaflet vs OpenLayers" talk

This blog post is a response to Iván Sánchez Ortega's "Leaflet vs OpenLayers 3" talk, which he gave at FOSS4G Seoul. I, as an OpenLayers developer, would like to defend OpenLayers and provide some comments that I think are important making.

Newbie Friendliness

To compare Leaflet and OpenLayers in terms of "Newbie Friendliness" Iván took the simplest tutorial of each lib and tried to create a basic OSM map centered on Seoul. The OpenLayers tutorial didn't make it clear that the longitude should come before the latitude in the array defining the view center, so Iván ended up with a newbie-unfriendly error message at map initialization time.

The OpenLayers documentation problem has been fixed since then. But in general I agree that Leaflet is more newbie-friendly than OpenLayers. For example, the notion of Coordinate Reference System (CRS) is explicit in OpenLayers. This is because we want OpenLayers to work with Web Mercator, as well as with other projection systems.

I also think one cannot judge friendliness with just one example. For example, it would be interesting to compare Leaflet and OpenLayers in terms of easiness of creating a map in a local projection, the Korean 2000 (EPSG:5179) projection for example.

Build sizes

Iván compares the size of minified builds (126 KB for Leaflet, versus 465 KB for OpenLayers). He also compares the number of classes and namespaces (52 for Leaflet, versus 163 for OpenLayers). Great! What does that mean? It means two things. (a) OpenLayers includes more built-in features than Leaflet. (b) OpenLayers users should create custom builds of OpenLayers, with just what their application needs. This cannot be stressed enough.

Iván does mention custom builds in his talk. He also says that creating custom builds requires using the Closure Compiler, and that this may « not fit with your toolchain ». In fact, if you use Node/NPM in your Javascript project, which is what a lot of Javascript developers use these days, installing OpenLayers will also install closure-util, which will download and install the Closure Compiler for you. So if you use Node, the only thing you need for creating custom builds is Java (a Java Runtime Environment).

And, about OpenLayers, Iván also says that « most integration tools (Angular, React, Polymer) or toolchains won't be able to slim it down without help ». I have to say that I have a hard time understanding what he means here. Do Angular and React include build tools that are compatible with Leaflet and not with OpenLayers? Sorry, I don't get it.

Iván also compares the size of unminified files (223.6 KB for Leaflet, versus 3.5 MB for OpenLayers). He's right. This is a problem, somewhat related to the use of the Closure Library. We are considering removing our dependency to the Closure Library, so we hope to fix that problem in the future.

For the record, we, at Camptocamp, don't use ol-debug.js at all. Instead we use an auto-loading mechanism where the OpenLayers scripts are individually loaded based on the dependencies tree. But this is a bit advanced.

Coding Patterns

The OpenLayers code snippet provided by Iván could be replaced by this:

var map = new ol.Map({
  target: 'ol3map'
});
map.addLayer(new ol.layer.Tile({
  source: new ol.source.OSM()
});
map.setView(new ol.View({
  center: ol.proj.fromLonLat([127, 37]),
  zoom: 8
});

So by using a more imperative style, you can get the same indentation level as the Leaflet code snippet. So I find Iván's arguments rather weak.

It is true that OpenLayers provides more classes, uses the Simple Features Spec (and GeoJSON) as the feature data model, and is generally more verbose than Leaflet. But this may also make your code more explicit. There are more important things in my opinion.

Documentation

Iván is correct to note that the 125 (and counting) examples OpenLayers provides are an important aspect. This is what users should look at to learn about how to use the library. The OpenLayers development team does a good job at adding a new example for every new feature, and maintaining all these examples.

It also true that OpenLayers' API documentation is verbose and imperfect, but it is comprehensive, always in sync with the code, and it includes relevant information. The OpenLayers team is committed to making the API documentation nicer and more convenient to users.

Map Rotation

OpenLayers has supported map rotation from day 1. It is a core concept of OpenLayers. Leaflet doesn't support it. So Iván created patch for this. Kudos to him! To my knowledge no pull request has been created yet. And reading this GitHub comment from Vladimir Agafonkin I am wondering if this functionality will ever be merged in Leaflet. Unless Vladimir has changed his mind, which would be fine!

3D

It's correct that OpenLayers alone doesn't support rendering 3D objects. But OpenLayers includes a WebGL renderer at its core, which already supports Image layers, Tile layers and Vector layers, although only Point geometries are supported at this point. So I think OpenLayers is in a good position to display 3D objects in the future, better than Leaflet. Iván's Leaflet.gl is just a (very nice) hack at this point, and I don't see it being merged in Leaflet any time soon. Maybe another challenge Iván will accept :)

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