Creating and Image Map in GIMP is very simple and you don't need any HTML knowledge. Sites like can do the same type of thing but GIMP has a built-in Image Map filter which I like better.

Open the image in GIMP and click on the "Filters" menu. Click "Web" (4th from the bottom) and select "Image Map..."
A new window will open up and this is where you actually create the image map.
There are 4 main options/modes on the left: Mouse, Rectangle, Circle and Polygon. The latter 3 create their respective shapes and the mouse edits existing shapes. These are the ONLY shapes you can make in image maps. To create a shape, click a starting place and then click an ending location. You must DOUBLE-CLICK to finish a polygon. Make sure that the shapes don't overlap. Paste your link into the URL space and uncheck the "Relative Link" box. Don't worry about selecting the Link Type because GIMP does that automatically afterwards.
To make a relative link, check the "Relative Link" box and type in the file path, name and extension RELATIVE to where the page containing the image map will be.
You can manually change pixel units in the next tab but the Mouse Editing tool works better. Finally you can create JavaScript statements to execute when the link is moused over/out.
All links appear in a list to the right. You can delete a link with the Trash Can icon or edit the info with the pencil and paper icon.
To save the map, click the Save icon. It will be a file with a .map extension but it's just a text file so you can rename it. Open the file in a text editor such as Notepad and copy the HTML code and paste it into your page. Gimp generates a few unessential lines of comments which you remove if you want.

Image Map Example: