[Community] Display text from shapefile or PostGIS into themouseover popup

Moisan Yves ymoisan at groupesm.com
Fri Dec 9 20:14:09 EET 2005

> Here's one use case:
> I have 1 shapefile for last 5 years showing projects done in that 
> particular year. The shapefile has field for contact information and 
> project url that I would like to be able to show to the users.  In my 
> case, I have just a few layers (country boundary, state boundary and 
> projects). I wouldn't want mouseovers for country or state. I could use 
> labels for those. However, it would be immensely useful to display a brief > project description in the mouseover.  This is a very simple use case 
> which I believe could be applied to all kinds of situations.

Popups do have the ability to make a map more legible since they hold information that otherwise would need to be burned-in as labels, so that's one good point about popups.  In order to strike a balance between what can be represented as a label and what would benefit from a popup (and to avoid label or popup overload), I'll venture a definition of a popup : 

Popups are more or less rich-content hyperlinked labels with visibility turned off by default.  

To me, the most important point is the hyperlinking functionnality.  A road name clearly only needs a label, unless you'd want to gain a url to some artifact related to that road ...  The second most important aspect of a popup is rich content.  For text only, use a label.  Although in your case, a formatted project description qualifies as rich content IMO at least due to it's sheer size (can't see how you could burn in a 3-paragraph long label).

Now, the hyperlink is needed in a popup (or is it; I guess you could just set it to void() ??).  I see this well in terms of *content* (managed by Plone), where an hyperlink to some content artifact or representation can be used.  But the popup can't point back to a shapefile, so in this case you'd basically want "[potentially] rich-content labels with visibility turned off by default".  

> Regarding overlib popups all over the place, we could have a flag to 
> enable/disable popups for a layer and an additional field to specify the 
> (dbf or PostGIS) field  to display in the popup. At any time, only one 
> popup shows over the map. 

I think a key in usability would be for the user to be able to explicitly tell PrimaGIS *not* to query the layers for attribute info.  For the moment, you have as many "popable info layers" as there are PrimaGISDataLayers in your map.  It could be useful to explicitly turn the pop up machinery off for any subset of DataLayers.  Maybe a "pan/zoom mode" could automatically toggle popups off so that they don't interfere with panning/zooming and don't make costly spatial db queries for attribute values ?  Then an "info mode" would toggle popup behaviour back on (e.g. tick all 'enable popups' checkboxes for DataLayers) and the user would have the opportunity to further deselect some layers to turn popup off.  

I suspect this would involve quite a bit of machinery, especially if one wanted to pass that behaviour along to "read-only" PrimaGISLayer objects which is the point you're making.  If you'd hyperlink to the project url, you'd need a map object (icon, sensitive polygon ...) that you can attach a url to.  In effect, that would mean that PrimaGIS be able to dynamically generate some map object that it can link a url to from data coming from an arbitrary datastore (shapefile, postGIS ...).  I still don't know what url you would assign to it, but in your case the url field could be used.  This is not the general case though and maybe a default could be a popup with a void() hyperlink. 

Having the possibility to select attributes to display would mean querying some resource (a shapefile, postGIS tables, WMS service) with some sort of GetAttributes function that would return a list of fields.  Implementation code to gather the info from within the datastores would need to be written.

> I see your point about having 10 layers in a map where a mouseover would 
> come up at every mouse movement. But that's fine. I don't think one would > use the mouseovers to substitute queries over the data in the map. They 
> would have to be used carefully by whoever is making the map. 

Which is another reason to be able to explicitly toggle off attribute-fetch behaviour IMO.  

That's it for now.



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