Firstly, make sure you have enough content to demand it's own website, if you've only done one map I'm not sure it requires a portfolio any more complicated than an interlopers one, but if you decide you want to, here are some tips:
You'll need a domain (www.whatever.com/.net
) and webspace (the server where the data is accessed from), each you can buy in year long blocks from any webhosting company.
But, before you do that you should have your website done. I use dreamweaver, but there are a number of free programs out there and you could even use notepad, if you learnt how to.
Have a look at some other portfolios and write a lsit of what you like and don't like about each, then use that to get an idea of what you want from your site. I usually mock it up in photoshop then build it from that, adding in any extra features along the way (java drop down menus, lightbox, etc).
Remember to design your site to be easy to update, you don't want to spend hours adding new content each time if you don't have to. Also be selective on the content, no one wants to see boring images on your site, it should be your best work.