How to Make a Simple KML file
(Using a spreadsheet to enter coordinates...)
A KML file is a text file with (among other things) a series of coordinates for creating markers at desired locations. KML files can be created / edited with a text editor (NotePad, etc.) and there are lots of examples that can be downloaded and used as templates (copy/paste).
You can also use a spreadsheet to enter the information, and then export that file to a text file, rename it with a .kml extension, and post that...
Excel would be a great program to use for this type of data entry, except that when you use Save As from Excel it wants to put many of the output fields into quotes (so instead of getting -121.3, 48.9 you get "-121.3, 48.9") - and these quote marks mess up the .kml file. (if someone knows of a way to get Excel to export without the quotes let me know...)
A Google Documents spreadsheet, on the other hand, will allow you to output a text file that is just a text file (no quotes). Thus, this How-to uses Google Documents.
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Download the Excel template spreadsheet: excel2kml.xls.
Edit the file NAME and Description.
Copy / Paste the 'Placemark' row as needed to create as many rows (placemarks) as you need.
Edit the Placemark data:
Then (when all edits are done), in Google Docs:
Import (File / Import...) the .xls spreadsheet
From the Share button, choose Publish as web page
For Sheets to publish, select Sheet1
Click Start publishing
Under Get a link to the published data, choose TXT (Plain text) - not 'Web page'
Copy the url link from the dialog box (it should be a long url string, ending in '&output=txt')
Paste this url into a new browser window
Download/Save this text file to your computer (a file with a .tsv extension)
Change the .tsv extension to a .kml extension
Post the .kml file for use in Google Earth or Google Maps...
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