I was recently asked to create an HTML page that would access a CSV file containing a list of latitude/longitude values and generate a map with markers for each location. This project was a proof-of-concept challenge for me so I’ve really just made a barebones implementation. That said, it should be very easy to expand using only Google’s API documentation for reference. Google Maps were the clear choice as they’ve become a bit of a de facto standard. Enough – let’s dig into the code!

This block of Javascript converts a local CSV file to a multidimensional array that can be easily accessed and manipulated within memory:

// This will parse a delimited string into an array of
// arrays. The default delimiter is the comma, but this
// can be overriden in the second argument.
function CSVToArray( strData, strDelimiter ){
	// Check to see if the delimiter is defined. If not,
	// then default to comma.
	strDelimiter = (strDelimiter || ",");

	// Create a regular expression to parse the CSV values.
	var objPattern = new RegExp(
		(
			// Delimiters.
			"(\\" + strDelimiter + "|\\r?\\n|\\r|^)" +

			// Quoted fields.
			"(?:\"([^\"]*(?:\"\"[^\"]*)*)\"|" +

			// Standard fields.
			"([^\"\\" + strDelimiter + "\\r\\n]*))"
		), "gi");

	// Create an array to hold our data. Give the array
	// a default empty first row.
	var arrData = [[]];

	// Create an array to hold our individual pattern
	// matching groups.
	var arrMatches = null;

	// Keep looping over the regular expression matches
	// until we can no longer find a match.
	while (arrMatches = objPattern.exec( strData ))
	{
		// Get the delimiter that was found.
		var strMatchedDelimiter = arrMatches[ 1 ];

		// Check to see if the given delimiter has a length
		// (is not the start of string) and if it matches
		// field delimiter. If id does not, then we know
		// that this delimiter is a row delimiter.
		if (strMatchedDelimiter.length && (strMatchedDelimiter != strDelimiter))
		{
			// Since we have reached a new row of data,
			// add an empty row to our data array.
			arrData.push( [] );

		}

		// Now that we have our delimiter out of the way,
		// let's check to see which kind of value we
		// captured (quoted or unquoted).
		if (arrMatches[ 2 ]){
			// We found a quoted value. When we capture
			// this value, unescape any double quotes.
			var strMatchedValue = arrMatches[ 2 ].replace(
				new RegExp( "\"\"", "g" ),
				"\""
				);

		} else 
		{
			// We found a non-quoted value.
			var strMatchedValue = arrMatches[ 3 ];
		}

		// Now that we have our value string, let's add
		// it to the data array.
		arrData[ arrData.length - 1 ].push( strMatchedValue );
	}

	// Return the parsed data.
	return( arrData );
}

This initialization function is all it takes to generate a Google Map and add all of our markers:

function initialize() 
{	
	// Set lat/long to center on the USA
	var lat = 39.8282;
	var lng = -98.5795;
	var zm = 5;

	// Configure the starting variables for the map
	var mapOptions = {
		center: new google.maps.LatLng(lat, lng),
		zoom: zm,
		mapTypeId: google.maps.MapTypeId.ROADMAP
	};

	// Generate the actual map
	var map = new google.maps.Map(document.getElementById("map-canvas"), mapOptions);

	var returnValue = "";
	var request = new XMLHttpRequest();

	// Read the lat/long info for markers
	request.open("GET", "zip-lat-long.csv", false);
	request.send(null);
	returnValue = request.responseText;

	// Convert our data from the CVS file to a usable array
	var data = CSVToArray(returnValue);

	for (var i = 0; i < data.length; i++) 
	{
		// Create a lat/long object readable by Google
		var myLatlng = new google.maps.LatLng(parseFloat(data[i][1]), parseFloat(data[i][2]));

		// Generate a marker from the lat/long object and add it to the map
		var marker = new google.maps.Marker({
			position: myLatlng,
			map: map,
			title:data[i][0]
		});
	}	
}

Using these two functions, all it takes to generate the actual map is a single line of code:

// Initialize the Google Map
google.maps.event.addDomListener(window, 'load', initialize);

You can see this code in action right here: http://sideapps.com/smart911/

If you’re interested in the CSV file it can be downloaded here: http://sideapps.com/smart911/zip-lat-long.csv

I must admit, I am a bit prejudiced toward web applications… However, I found Google’s API and the small amount of Javascript I had to learn very pleasant. I anticipated a much longer process and was very happy to be able to complete the task so logically and directly. Hopefully this helps someone out!