So, apparently at WhereCampEU this weekend, there was some discussion of “Why people use web mapping libraries other than #openlayers”. (I can’t find any other references to this in Googling; someone who was there may be able to provide more context which might alter the content of this post.)
There are a number of good points about OpenLayers identified in the whiteboard snapshot; the ones listed there that I can read are:
- Default Look
- Examples are not Good
- No explanation of the general architecture
(Throughout this post, I will be comparing OpenLayers to other mapping tools listed on the whiteboard snapshot; with the exception of “Leaflet”, which I can’t seem to find by googling things like “Leaflet” and “Leaflet web mapping”. Help is gladly accepted.)
Some of these things I would be interested in understanding more deeply — and some I’d like to take on trying to address.
Documentation and Examples Are Not Good
I think a large difference of opinion exists between different people in the OpenLayers using and developing community about how documentation should be managed. In general, in OpenLayers, we have taken the approach of saying that the best form of documentation is via examples that clearly demonstrate how to use a given set of functionality. (Note that in this case I say ‘we’, but I won’t claim this is a considered decision on behalf of the project. Instead, it is one that I believe fell into place in large part because of how we started documenting the project, and has not drastically changed.)
In OpenLayers, the examples are the first line of documentation. Always check the examples first; not doing so is doing yourself a disservice. This is not to say the examples are perfect; they are far from it. Especially as the project has grown, the examples are not an ideal way to understand all of the functionality of OpenLayers; as the library has grown, the complexity has grown correspondingly. However, I have often been told “Well, I looked at the API docs first and they weren’t clear about how I was supposed to use a specific feature” — and I think that particular approach is one that is doomed to fail with the documentation currently available in OpenLayers. The best advice I can give to beginners starting with OpenLayers is: start with the examples. Search for the thing you’re looking for — and if you can’t find what you’re looking for with the search term you’re using, tell the OpenLayers users list.
Now, as I’ve said, the examples haven’t kept up. OpenLayers has grown tremendously, and although we are relatively diligent about writing API documentation, prose documentation has never been high on our list, and prose documentation outside of the examples probably never will be. I think that this is a problem that really needs a solid champion outside of the current developer pool if any progress is going to be made; no one on the current development team is likely to be strongly in favor of making sweeping changes, simply because the choices are to continue to add features — things like improved performance, better mobile support, improved functionality for new features like geolocation APIs — or to work on documentation, and the current developers will tend towards the former.
That said, I think it’s fair to compare OpenLayers to some of the other mapping APIs listed on this point.
- Google Maps: Blows OpenLayers out of the water on API documentation. Google has done an excellent job of integrating reference documentation with prose documentation, and has literally hundreds of pages of API docs for their mapping APIs. Their examples are solid — though comparing this page to the OpenLayers equivalent seems to have a certain something lacking. There is, however, no doubt that Google has done great work on documenting their API, and that there are many simple problems for which Google is a better solution than OpenLayers for some users simply because it’s better documented.
- Polymaps: Again, a relatively well done set of documentation. Their API docs are much more descriptive than the equivalent in OpenLayers, and their examples like this one provide a simple, easy to read overview, example, and code in one page, and the example overview is quite nice, with screenshots. I think that this is well in line with what you would expect from Stamen. I will say that their API docs do lack information about what properties you are actually supposed to pass into functions; the map documentation for example, says that “map.center([x])
Sets or gets the location of the map center. If the argument x is specified, it sets the new map center”… but doesn’t explain what x is supposed to be. So long as functions have clear examples, this probably isn’t a problem; it’s just something that I could see being a problem with more complex functions that don’t take obvious arguments.
- Web Maps Lite (I’m assuming this is the Cloudmade offering): This API offers a pretty reasonable set of documentation; their Overview is slightly more comprehensive than the OpenLayers equivilant which uses Naturaldocs. I would describe most of the brief API method descriptions as being similar in quality to those in OpenLayers; no obvious winner or loser there. The examples seem clear and well done for the few that exist; not particularly comprehensive or entirely obvious, but probably a win for most simple use cases over OpenLayers.
- Mapstraction: Documentation was a bit hard to find; I didn’t even see it linked from the homepage, but Googling turned up javadoc-like content; limited, but since Mapstraction is a pretty simple library, probably not insufficient. The examples are… brief, but workable, looking at the mapstraction sandbox. I’m not a huge fan of the sandbox form of examples personally, but for people who are, this probably is a perfectly workable set of docs — but I don’t think there’s an obvious win over OpenLayers here.
- Tile5: The Tile5 API documentation seems, to me, to be less informative and more confusing than OpenLayers. It seems hard to navigate, and even once you’re in it, it’s hard to understand exactly what you’re meant to do with things like T5.Marker objects. The ‘examples’/tutorials section has two sections, approximately equivalent to the OpenLayers introduction, but nothing further; it’s not clear that these examples offer any sort of view of a more comprehensive idea of how to start using the library. I may be missing something, but I feel like this is actually a pretty major lack in this particular project — and given that OpenLayers is coming from deep in the hole on this problem, that’s saying something
Unfortunately, without being there, it’s hard for me to know what people want here; I’ve heard requests for a general architecture description before, but when I try to give them, people usually end up saying something like “No, that’s not what I meant, I wanted something… else.” I’d be interested to hear thoughts on what this means.
In general, the architecture of OpenLayers is: You pass an HTML element to OpenLayers, at which point, it owns that element. You inform OpenLayers of a set of x/y coordinates you would like to render data into, and it takes layers of content, and allows you to lay down multiple layers in whatever set of x/y coordinates you defined (via your base layer). In general, OpenLayers tries to provide comprehensive tools for interacting with the map — using browser gestures, clicks, etc. — with an API to implement more advanced functionality beyond that. Where possible, OpenLayers will make it as easy as practical to interface with a wide variety of data sources to provide the data you are able to browse, and make interacting with the map to increase the amount of data possible.
Beyond that, OpenLayers isn’t supposed to be much of anything; it’s an API and a tool for rendering map data, and little else. (Sometimes the problem is simply overly high expectations for OpenLayers because people have used it to do a lot of complex things!)
In searching out the various map APIs described above, I didn’t see anything obviously filling this role, which probably means that I don’t know what I’m looking for — but I’d be happy to learn, and explore how to solve this problem, because it doesn’t really sound that complex to solve.
Default Look and Feel
This one is interesting. In general, OpenLayers doesn’t *have* much of a look and feel; in fact, the default look and feel is generally limited to 7 icons which are easily replaceable by CSS. (One of the things we even have docs for!) That said, I’m willing to go head to head against most of the other APIs here for that issue:
- Google: Google has smaller controls than OpenLayers; these may be more attractive to some people. I’m willing to accept that some people prefer Google’s style to OpenLayers standard control styling.
- Tile5: When I look at Tile5’s example at simple map marker, the only ‘default style’ I see is a checkered grey and black background (easily implemented via CSS in any webpage).
- Polymaps: Seems to have a default +/- icon, but no others; the +/- look very similar to what we have in our mobile example, styled using entirely easily-modifiable CSS.
- Mapstraction: This uses the native control style for everything, it looks like, and turns controls off by default; since OpenLayers can have its controls turned off with one map option, this feels like they are the same in this regard.
- Cloudmade: basic example seems to have no default look at all; again, no difference.
Overall, it seems there is a preference for… no controls. Perhaps we should simply make that a better-documented OpenLayers mode of operation, and then people could complain about how their map didn’t have any default styling
Edit: After reading Volkler’s post on the topic, I realized that this point was *Usability*, not Viability. I’ll expand on that after this section, but I think that the Viability section here is an important concern, if you ignore the off-base ranty nature of it: OpenLayers is an extremely broadly used and widely supported tool, so using any other open source solution is risking joining a smaller community, which may have its own dangers.
This is the one I actually have the strongest feelings about. I think that if you are going to talk about problems with OpenLayers, viability is the one that has the least of a leg to stand on, on any API other than a commercially supported (non-free) one.
- 2000 members of its users list, with dozens of messages a day.
- Code contributions from more than 40 users
- New releases multiple times a year, closing hundreds of bug reports
- A steadily growing list of features and enhancements
OpenLayers is the de facto web mapping library used by almost every open source geo related project. OpenLayers has a broad community, with broad support. There are two books introducing OpenLayers, there is an active community around OpenLayers, and earlier this year, more than a dozen organizations came together to sponsor an OpenLayers code sprint, funding 18 developers to stay in Switzerland for a week and work solely on supporting OpenLayers.
OpenLayers is a huge success story. The biggest evidence of that, in my mind, is simply the fact that no one talks about using OpenLayers anymore — they just do it. OpenLayers has become the de facto web client at FOSS4G; OpenLayers is used by tens of thousands of people every day around the world, from OpenStreetMap to the US Government, to the Portland public transit system, to consulting companies selling services in Australia.
I’m sure that there are many people who would claim that other APIs win on various aspects — and they’d be right. Documentation is a pain. Since OpenLayers caters to thousands of different use cases, it’s not as trivial to get started with. The library is complex, and there are many features that are confusing and complex to get started with — but overall, OpenLayers is a reasonably usable library for doing a relatively complex task that achieves in a way that I don’t think any of the open source competitors come close.
Someone questioning the viability of OpenLayers makes me wonder what they mean — because the project continues to make regular, large strides in new developments and features, and I can’t see how anyone could look carefully at the project in comparison to its competitors and think that it fails on that merit.
I’d be glad to here about this point, or any others, from people who were at the WhereCampEU session — perhaps I’m misunderstanding the complaint, for example — but I would say that to almost everyone looking to create a web map: OpenLayers is a strong starting point, if you’re a competent developer, upon which it is possible to build great applications.
It appears that “usability” here is a description of the API as it applies to developer usability. I think that this is an area where the main problem is “OpenLayers is a broadly used library supporting dozens, or hundreds, of different use cases, and is not a narrowly designed tool designed to solve a specific problem.” I’ve theorized for a long time that a lot of people (especially people who are likely to attend WhereCamp events) would be much happier with OpenLayers if I were to write a simple “OSM.Map” wrapper around it that picked sensible defaults for users of OSM maps.
The biggest thing that makes usability hard is targeting too many users. OpenLayers is trying to solve many hard problems — from integrating with OSM and parsing OSM data, to integrating with OGC catalog services, to interoperating with WFS. The most ’sensible defaults’ for one application are not the best ones for another, and with weak documentation, usability suffers.
Some ways to fix this include better docs, writing wrappers for specific purposes to simplify defaults for some users, etc. But overall, because OpenLayers is a library which supports many different use cases, it’s somewhat harder to get started with for all use cases. This is unfortunate, but not unexpected; I think it’s a necessary evil of having an API which targets such broad use cases.
Overall, many of the complaints about OpenLayers are reasonable: our documentation is weak, our default styling apparently doesn’t appeal to some people (I still like it, but I’m apparently in the minority), and it’s harder to get started than with some other tools. However, we’ve seen continued transitions of people from other tools to OpenLayers as they encounter harder problems — because as your problems get harder, OpenLayers becomes a more attractive solution to prevent you from having to reinvent the wheel.