Usually we use areas to point some fill on the passages, be it water, sump, clay, sand… Areas are limited by lines. These lines can be of any type, but they must intersect. To be sure that lines really intersect, it's better to draw lines beyond passage walls. This out-limits parts will be clipped. The same effect can be achieved inside passages by using line type border with “-subtype invisible” option.
Remember that Xtherion will use last type you choosed as default value for next areas to create. So the fastest way is to define all areas of same type (e.g.: water), then change type (e.g.: clay) to define all your clay areas, and so on. As usual, you'll find an area “type” menu in “Area control” panel.
To insert a new area, press Ctrl-A or walk the usual way to “File commands” panel, choose “Insert area” from “Action” menu, and press what is actually the “Insert area” button. Area control panel will open automatically and you'll be in “insert area border” mode, as stated by the red box at the bottom of the window. Now you can click succesively on lines that work as a concrete area borders. You need to proceed clockwise or counterclokwise. This is, you need to click succesively on lines that intersect. If you clicked in two border lines that don't intersect, you'll get unexpected behaviour.
Notice that, when you clicked on a line, it gets listed in Area control panel as e.g.: 12-268-340. This is line's name (ID) as assigned automatically by Xtherion. Since we created these lines, they remained unnamed and it was fine, but now that we want them to be listed as area borders, they need a name. If you go to “File commands control” panel, you'll see that new name is displayed in selected lines. You can rename a line to a more descriptive name by selecting it, going to “Line control” panel and editing the ID on “ID” textbox.
Back on the “Area control” panel, you can click a name in the list and press “Delete” button to get it out of the list. “Deleted” lines will not be removed, simply they aren't treated as area borders.
When all borders for a concrete area have been listed, press Esc key. You'll be back in “Select object” mode so you can press Ctrl-A again to begin to define another area, or click on any object to select and edit it. However, it's not possible to click an area on canvas. You must go to “File commands control” panel, and click on the appropiate line to select an area. One of the borders of the area will become the selected thing on canvas, so you can see if this is the area you are effectively looking for.
If you don't realized it yet, the same is true for lines and points too. If you click an object line in “File comannds” list, the object will be displayed on canvas as selected. If you select an object on canvas, its line in the list will we displayed in grey. Other panel lists work the same way, e.g.: line point list on “Line control” panel.
To delete an entire area, select it on “File commands control” panel and press Ctrl-D, or choose “Delete” from “Action” menu and press what is actually the “Delete” button.
For a complete listing of area types and options that apply, see thbook.pdf. You'll find it on pages 23 and 24.