I'm writing a blog which is currently hosted at Wordpress.com. My blog posts often contain content from different cities in my country. Now I'd like to include some kind of geoposition in my blog. Furthermore there should be another site with a map (optimal solution would be an OpenStreetmap) and markers which are at the geoposition and link to that specific post. Currently I have no idea if this is possible at all and how to realise it. How can I realise it?
Since your blog runs on wordpress.com, your options are limited.
In order to render the map, you need the data in some form that the map can process it. Either addresses or geocodes.
In order to generate the map dynamically without manual interference, these data need to be saved with the post, and somehow retrieved.
With wordpress custom fields you should be able to save those data. This functionality is only available as VIP:
Also, as far as I can see the plugin support at wordpress.com is limited.
The only thing that comes near your desire is the use of google maps, but as far as I can see I am afraid you will have to insert the markers manually. See: "embed a Custom Google Map into your WordPress.com blog":