CSV to KML Converter

KML's coordinate syntax is unforgiving in a specific way. A tuple is longitude,latitude,altitude, comma separated, with no spaces inside the tuple. Separate tuples are separated by whitespace. So a line is -0.0877,51.5079 -0.0962,51.5071, and the spaces and the commas mean opposite things.

Two errors follow from this and both produce a file that opens without complaint. Putting a space after the comma splits one coordinate into two malformed ones, and Earth quietly draws nothing. Putting the latitude first plots your point somewhere else on the planet, and Earth quietly draws it there. Neither is an error message. You find out by looking.

This converter reads your headings, works out which column is which, and writes the tuple correctly. If your columns are named latitude and longitude, or lat and lng, it needs nothing from you. If they are named something else, the dropdowns list the columns of the file you just loaded and show which one was picked, so what is on screen always matches what is about to be written.

The quick way to get a row's data into a placemark is to concatenate it into the <description>, usually as an HTML table. It renders, so it looks like it worked. What it costs you shows up a week later.

A description is a blob of markup. Google Earth cannot filter on it, My Maps cannot use it to style your pins by category, and converting the file back to a table hands you one column of HTML instead of the eight columns you started with. Our own KML to CSV converter has to run a rescue routine to unpick exactly this, because Google My Maps writes its exports that way.

<ExtendedData> with one <Data name="..."> per column is the structured form. Earth renders it as a labelled table in the balloon by default, My Maps reads it as the layer's columns and offers each one for styling and filtering, and a round trip back to CSV returns exactly the columns you started with. The description element is left for the column you actually want as prose, which you choose separately.

KML is XML, so five characters cannot appear literally in a value. A store called Fenwick & Sons and a note containing <br> both break the document if written straight through, and a broken KML does not open at all: Earth shows a parse error and stops. Every name, description and data value here is escaped, so the output is well formed whatever is in your cells.

Rows without a usable coordinate are left out and reported. The warning gives the count against the total and lists the first ten by their line number in the source file, with the value that failed:

3 of 128 rows had no usable coordinate and were left out:
row 19: coordinate cell is blank;
row 44: "N/A", "2.35" is not a number;
row 91: longitude 512000 is outside -180 to 180.

That last one is the most useful line in the tool. A longitude of 512000 is a projected coordinate in metres, which means the whole file needs reprojecting to WGS 84 before any of it can become KML. Being told immediately beats opening an empty map in Google Earth and working backwards.