I have no experience with web crawlers -- but I know that Apache maintains an open source web crawler called "Lucene." How would I go about writing such a crawler to search the web for geo tagged data close to a particular location? What would a general road map look like? How do I pick which slice of the web to crawl? Do I use regular expressions to find things that look like longitudes and latitudes? What does a general sketch of that solution look like?