google mapskmlpolyline-creation
I have many markers in a kml file. All the markers are on the roads.
I wonder if there is a way to process the data and connect the markers by following the road? Of course, the markers should not be randomly connected with each other. The point is to mark the parts of the roads that have markers on them.
I could of course just manually create the lines myself. But there are so many markers, and the data is expanded almost daily.
Merging your truck routes data looks complex, and it is maybe not necessary. Another approach could be the following:
Retrieve some road network data for your area of interest. Maybe you already have it. Otherwise, you could get openstreetmap data on roads.
Link or snap your route data to this network using some basic data matching operations. A simple linking rule based on minimal distance should provide a satisfying approximation.
For each section of the road network, the number of times each section has been driven will then be derived easily: it is the number of truck routes linked to it.
If your purpose is mainly to display your data to have an overview of the distribution of your truck moves, you can also simply display your data using transparency like on this image:
KML is an OGC standard so there should be a lot more applications now a days which will allow you to "export to KML".
OpenLayers makes it very easy to READ and WRITE KML files using Javascript Code.
GDAL will also allow you to READ and WRITE KML files in command line. For example: create a KML file from a Spatial Database Query.
EDIT: You can also export to KML from ArcGIS 10
EDIT #2 Google does not give you the ability to download KML from it's map data. It does provide some map web services but they are not what you are thinking.
ESRI and many others do host map services for free though. For example: http://services.arcgisonline.com/ArcGIS/rest/services/Reference/World_Boundaries_and_Places/MapServer
Notice at the bottom of the above page you can "Generate KML". But what's better, this is a REST service you can query straight from code.
Best Answer
AFAIK Google Maps API won't give you access to its underlying vector data. You can use OpenStreetMap instead (which does provide its vector data, and this is often not understood by people). Unless you have vector data, there is no reliable way to match your markers with roads.
You could match each of your markers to the nearest road (using a certain distance tolerance). Then you can simply highlight the roads that have a certain density of markers.