I have used Google Maps a couple of times, but what wondering about [OpenLayers][1].
&lt;br&gt;Before starting any kind of coding, here are a couple of questions that come to my mind,

 - Why would I use OpenLayers instead of Google Maps?
   - Except for its OSS licence, anyway
   - Did you encounter any situation in which you&#39;d recommend absolutly not using OpenLayers?
   - I did a [search about &quot;OpenLayers&quot; on Stack&amp;nbsp;Overflow][2]; there are not many answers. Does it mean this solution is not used much? Could it be a problem for long-term viability of the project?
 - For those of you who have already used OpenLayers: are there any common pitfalls / problems I may encounter?
   - What about using a JavaScript Framework with it? I&#39;ve seen it&#39;s using [Prototype][3], and I know Prototype, so that would be OK. But what about using something else like [MooTools][4]? *(Which is not compatible with Prototype, BTW)*
   - Are there any kind of speed and performance related problems? I need my application to be responsive and can&#39;t wait hours to get a map displayed.
 - Are there maps available for many places, or are there lots of those missing?
   - That is, I&#39;m in France, and need my application to work at least for big cities... Will that be OK?
   - if not, is it easy to find layers and visualisations for OpenLayers and integrate them?
 - Is there any kind of API to display roads? 
   - For instance, to show roads that are one-way only.
   - If yes, how can I do that? Do I have to have some kind of file containing those roads information, and, then, display them on the map by myself?
 - Do you know any good tutorial to OpenLayers?

I have not tried it yet, those are just out of the blue questions... 

  [1]: http://openlayers.org/
  [2]: https://stackoverflow.com/search?q=openlayers
  [3]: http://en.wikipedia.org/wiki/Prototype_JavaScript_Framework
  [4]: http://en.wikipedia.org/wiki/MooTools


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OpenLayers vs Google Maps?