What is KML?
KML is type of markup language based off of XML.
Stands for Keyhole Markup Language
Developed by Keyhole Inc. Google
KML files are very often distributed in KMZ files, which are zipped KML files
with a .kmz extension
Origin of KML
KML was first known as Keyhole.
KML originally developed for use with Google Earth.
Its development was engineered by Keyhole, Inc which Google acquired
Keyhole Markup Language (KML) is an XML notation for
expressing geographic annotation and visualization within
Internet-based, two-dimensional maps and three-
dimensional Earth browsers
In Other Words
KML is a way of displaying geographical data in an Earth Browser such as,
KML includes features that allow it to display:
<?xml version="1.0" encoding="UTF-8"?>
<description>New York City</description>
<name>New York City</name>
KML file types are used by programs such as:
Live Search Maps
Microsoft Virtual Earth
Everything is an “Object”. (Everything
inherits from the abstract “Object” KML
There are abstract elements
Everything is a tag:
The more advanced tags are (usually) for
Google Maps supports a subset of
Google Maps supports…
KMZ (compressed KML, including attached images)
Polylines and polygons
Styles for polylines and polygons, including color, fill, and opacity
Network links to import data dynamically
Ground overlays and screen overlays
KML is in XML format
Usually everything contained in
Can have multiple Folder tags to
separate different kinds of data.
For example, one folder containing
KML to show locations of pictures
and another folder containing KML
to show your path through the day.
The easiest element in KML.
A simple point on the map. It only needs a name and a location. You can
give it a description too.
Placemark tag defines the place mark
A Point tag within it defines where the Placemark will be.
A “type” called coordinate defines the Point.
Coordinates in KML are given long,lat. When typing in coordinates directly
into Google Maps, they are given lat,long. Be careful!
You’ll probably want to do HTML within the description tag.
You need to use the CDATA tag for this. If you don’t, your HTML’s tags
need to use entity references:
Can define a path using the Placemark tag and the
LineString tag instead of the Point tag.
Multiple coordinates. Again by long,lat,alt.
“extrude” tag makes the line go down to the ground
“tessellate” breaks each line into multiple pieces. Good
for long lines so they don’t end up underground.
0 = false, 1 = true
KML Servers must follow certain rules
Must return response code of HTTP 200
The type itself is:
Can set the type in PHP with:
Body must contain valid KML data and the XML declaration:
<?xml version="1.0" encoding="UTF-8"?>
Similar to CSS/HTML styles.
In a Style tag. Each style tag can have multiple styles within it: LineStyle,
PolyStyle, ColorStyle, etc.
The tag has an “id” so it can be referenced within a file or from another. (A
Global KML Style file perhaps?)
Add a styleUrl element to use a style.
HW2 could have different icons based on content? A site that grabs all
the Google Map icons:
Add an image to the Google Maps/Earth window.
Could be used for whatever purpose you like.
overlayXY and screenXY line up the image to the actual map
In this example, (0,1) (in fractions) means 0% of x (all the way to the left)
and 100% of y (all the way to the top). The upper-left of the image is lined
up with the upper-left of the map. The unit can also be determined by
Size tag (obviously) controls size of the image. 0 means to maintain aspect
ratio, -1 indicate to use native dimension. Using some other value makes
the image that value. For example 0.2 with units on fraction makes the
image take up 20% of that dimension.
Allows importing of KML, KMZ, and image files for ground/screen overlays.
Local or remote file
Uses a Link tag
Good way to split up large KML file into much smaller KML files. More
More interesting feature: can use scripts to generate KML data on the fly.
(PHP, Perl, etc.)
Usually uni-direction data flow (server to map) but when using
“viewRefreshMode”, the map can pass the script information on what is
being viewed (the LatLon box). Google Maps/Earth will call the script with
a BBOX parameter. Look at the KML Tutorial for more information.