Image via CrunchBaseBecause twitter limits the length of any post to 140 characters, a plethora of URL shorteners have popped up. This allows you to shorten a really long URL to something relatively short like http://tweepml.org/NCI-designated-Cancer-Center-on-Twitter/ to http://bit.ly/NCI_CC_List (because I made this one a vanity URL, it's a little longer than it would normally be). This is handy when you are trying to conserve every character.
One of the better URL shorteners, IMO, is http://bit.ly. If you have an account on bit.ly you can track the number of people who have clicked on your link since you tweeted it (click-throughs), where they are from (identifies generally geographic areas / countries) and when they clicked on your link. It's a great tool.
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