This page gives a quick overview and a few tips on how to add custom KML overlays to the maps within the Hot Air app.
KML is a file format used to display geographic data in an Earth browser such as Google Earth, Google Maps, and Google Maps for mobile devices. KML uses a tag-based structure with nested elements and attributes and is based on the XML standard. (See Google's tutorial for more information)
Hot Air map overlays support a subset of the KML tags. The following KML types are supported: Style, LineString, Point, Polygon, and Placemark all other types are ignored. Since all other types are ignored it is best to omit them from your overlay files to decrease how long it takes to load the overlay files and how long it takes to draw them on the maps within the app.
You can create the KML files using a simple text editor (which may be the easiest for very small files) or you can use Google Earth (which is free to download) to create or edit files on your computer.
I created the example overlay files by modifying an airspace data file from this site: http://www.lloydbailey.net/airspace.html. Then I followed this generalized steps: (1) opened the file in Google Earth, (2) created a new places folder to copy all the airspace data I was interested in, (3) then I expanded the subfolders of the loaded airspace data file, (4) I zoomed in to the area I was interested in and clicked on an airspace object I was interested - which highlighted the object in the Places listing on the left-hand side, (5) I then copied this object and pasted it into the folder I created in step 2, (6) after that I repeated steps 4 and 5 until I had all the areas I wanted, (7) next I went through my folder and deleted all the 3D objects and just left the 2D outlines and some of the placemark names, (8) finally I right clicked on my folder and exported (Save Places As...) the file as a .kml file. At this point the file was ready to upload to the app (you may also want to re-open the file in Google Earth to make sure it is correct and also check that the file size is small enough).
IMPORTANT: Be careful not to delete or modify the .sqlite file it stores the flight log data as well as all the other data the app needs to function properly. If you delete or modify this file you may loose information or the app will not function properly. You may be able to restore this file from a backup of your device.
To add the overlay files to your iPhone/iPod/iPad you must first connect it to your computer. Then open iTunes and select your device in the iTunes Library. Next click on the Apps tab, and scroll down to the File Sharing section. You will see a list of apps that use File Sharing. Click on Hot Air and you'll see any files you've already added, the database file that stores your flight log information ( the .sqlite file), and possibly some .kml files that were created when exporting data to e-mail within the app.
There are two ways to add .kml files to the app. Click the 'Add' button, navigate to your .kml file in the dialog box that appears, select the document, and then click Open/Ok. When you click sync, the file will be copied to your device. Alternatively, you can simply drag-and-drop a file onto the File Sharing list when the Hot Air app is selected. The drag-and-drop method immediately copies the files to your device without having to hit the sync button.