Google Maps
This was job which I did at the beginning of 2012 for Trail WIKI, I'm documenting it here because it involved many different interesting aspects and also included some useful information which will help with later jobs.
The wiki contains many pages which represent hiking trails. It uses an infobox template to that various information about each trail such as its distance, elevation and other attributes can be contained in a structured way in the article.
On the main page is a Google map which has markers for all the trails, and when one is clicked a popup is revealed containing a link to the associated trail article.
The client wanted to have this map functionality extended such that the infobox that pops up is customised to the style of the site and contains some of the key information from the trail article's infobox. Also he wanted to use the Semantic Maps extension so that he could have other maps throughout the wiki which shows only very specific sets of markers such as trails with a certain region or above a certain elevation.
Another issue is that the wiki will eventually contain thousands of trails, so the maps need to load the trail location data after the page has loaded, and the popup boxes in the markers need to load their content on-demand too.
Contents
Semantically annotating the infobox template
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Retrieving the location data via AJAX
Creating a custom popup box using the overlay method
I started with this script from the exampled in the Google documentation.
Populating the popup box with data via AJAX
Selecting markers with SMW queries
This was achieved by allowing a query parameter to be added to the #ajaxmap parser-function that contains a SMW #ask query (or in fact any other kind of query that produces a list of title links as a result such as DPL). These article titles are then extracted out of the resulting list and included in the ajaxmap_opt array defined in the JavaScript for that map. The JavaScript Ajax request then includes these titles in its query parameter when it asks for the location information.
This is not perfect because the list of titles should not have to be sent to and from the client, it would be better for the Ajax request to send just an identifier that the PHP can use to perform the #ask query then rather than performing it when the parser-function was first expanded.
Finishing up phase one
Marker clustering
A new requirement has been added to help speed up the rendering of the maps with many markers. The idea is to combine markers that are very close into a single cluster that works similarly to the markers that are in identical positions (due to multiple trails starting at the same location). The proximity is in terms of pixels though, not geographic distance, so the clustering depends on the scale.
A function would be added which transforms the location data (an list of geographic locations, each containing a list of trail titles) into a new list of the same format, but with the geographic locations merged if their current pixel distance is less than a certain amount. There should really be an additional array of pre-defined named-regions that could be made to apply above a given scale. The region title would be used in the title bar of the popup box instead of the first trail title.
This function to transform the data that the markers are based on would be called when the data is first collected, and again whenever the scale changes. The function needs to detect which markers are affected and create/delete them to match the new locations table. It would do this by creating the new data in a temporary table, then updating the markers by comparing the new transformed table with the last transformed table and then making the new table current.
Another useful addition would be to allow this transform to separate out the trails that start at identical locations into a circle so they can be seen separately at a small enough scale.
