How do I create a KML map data file?

You've got me on that one. In fact, I ended up writing a shell script that accepts a set of street addresses and outputs a KML data file suitable for importing in Google Maps or any other mapping system that supports the KML data file format. It's too complex to share here, however, (it's actually for a book I'm working on, but that's another topic of discussion!) but I can show you the rudiments of KML data files so you can easily copy and paste to produce what you seek.

At its most basic, KML is just a specific type of XML data file, which means that it looks a lot like HTML, the language of Web pages. You can learn more about XML in a lot of different places, but here's a link to the Wikipedia entry on XML as a good place to start.

Let's just jump in. Here's what a very succinct one-data-point KML file would look like:

Pretty confusing, isn't it? Let me show it to you again, but this time I will change the information that is related to the specific data point (an address on the Walt Disneyworld property in Orlando, Florida, btw!):

Not so bad once you look at that. Now let's change it once more, but this time add helpful prose for the name and description:

NOTE: Here's a weirdness you should know if you want to try and put all the pieces of the puzzle I've presented together, though: while the KML files are in long/lat order, the data you enter into Google Maps on a search to get a point plotted are in lat/long order. In other words, if you were to just copy and paste the point coordinates shown above, you'd end up not on this Earth. You can't just map -81.561995, 28.357403, in other words, you need to reverse the order of the two if you want to just search for that point in Google Maps: 28.357403, -81.561995. I have no idea why they aren't consistent!

If you'd like, copy the KML snippet above, save it as "sample.kml" and feed it to Google Maps to see what happens (as I explain here: Import KML data files into Google Maps).

But what you probably want is to have more than one data point in the KML file. This can be done by duplicating the "Placemark" block of KML. To illustrate this, I'll go back to the uncommented KML file (so it's a bit shorter):

See what I've done here? Turns out you can easily duplicate this material again and again, though it's a wee bit tedious.

Finally, here's a simple three-point KML data file you can download and examine for yourself that will illustrate the points I've made here. I hope it's interesting: wdw.kml (right-click or cmd-click on it and choose "save link to file").