An area is a portion of the cave filled with something. For example a pool of water is displayed as an area of type "water" (or "sump" if it is a sump). Other graphical elements are areas because they fill a region of the drawing: "sand", "debris", "mud", etc.

An area is defined by the lines that make its contour. These must intersect two by two, and must be listed in order, either clockwise or counterclockwise. If the lines do not intersect (ie, they do not define a closed contour) the result is unpredictable. When you draw the lines of the border of an area (type "border"), either visible or not (subtype "invisible"), you should extend them a little beyond the walls of the cave, to be sure that they intersect. Infact therion does not draw the portions of line that extends outside of the cave outline (which usually is defined by the cave walls).

To insert a new area, ie. to switch to insert area mode, select the menu "Edit | Insert - area", or the shortcut Ctrl-A. Each line over which you click is added to the list of lines that makes the contour of the area. When you are done press "Esc" (to switch back to selection mode), or Ctrl-A to inert another area.

Be careful not to click twice on the same line, otherwise it appears listed twice in the arae contour. You see this in the "Areas" control which displays the list of the lines of the contour. If a line is repeated twice (incorrectly), you should drop it one time so that it appears only once.

You can drop a line from the contour of an area. Select the line and press the button "Delete" in the "Areas" control. The line is dropped from the list of the area contour, but it is not deleted from the drawing.

The only way to select an area is through the "Objects" control, by clicking on the entry of the area. You can notice that a line of its contous appears selected in the window.

Although therion supports areas with border defined by several lines each intersecting the previous one, it's better to draw a single border line and define the area using only that one. Remember that therion clips objects to the outline, so the border line can extend outside the outline, and the area will not appear there. The reason is that the lines that border an area must have an id, and therion assigns one to the lines that do not have it when you define the area. he area border is just the list of these ids. If later you split the line into two, the original id is lost, but the list of the area border is not updated. As a result the area reference an id of a line that does not exists any more and therion raises an error when the project is compiled.

Nevertheless there are cases when multiline borders are necessary. For example, if you need to draw two areas that share part of their border, at least one of the two must have the border made of two (or more) lines.

The "area" command has as argumemnt only the type of the area. This can be one of the following

• "water", a pool of water
• "sump"
• "sand"
• "debris"
• "blocks"
• "snow"
• "ice"
• "clay"
• "pebbles"
• "flowstone"
• "moonmilk"
• "dimensions"
• "bedrock" (used to hide portion of an "underlying" area).

The area "dimensions" is used in map export from centerline only (no outline in the scrap). If you have dimensions data (LRUD) specified with centerline, and you export map from centerline only (no outline in the scrap), it is exported using this symbol. See morphing sample images.

Some areas (sand, debris, blocks, snow, ice, clay, and pebbles) are rendered by randomly placing picture elements in the reagion of the area. If this is too small, no element may be displayed. Others (water, sump, flowstone, and moonmilk) are rendered by filling the area region with a pattern. The rendering of the areas is shown in the figure below, taken from the samples in therion distribution.

The options of the "area" command are

• "place" defines the level on which to draw the area. It can be "bottom", "top" , or "default".
• "clip" specifies whether the symbol (of the area) if clipped to the cave outline or not. It can be "on" or "of".
• "visibility" can be "on" or "off".
• "context" displays the drawing of this area as if it were another type of area.

The exmple below has an area of type "water" bordered by lines of type "wall" and "border". One of the "border" lines, the one in the lower part, has the option "-visibility off". The area has the context "-context line wall:debris". The outcome is that the area is drwan with the "debris" symbols on its contous, and the "water" is not drawn. To draw the "water" you can add a second area with tha same contour, but without "context". If the area with the "context" is above the other in the list of the "Objects" control, it is drawn above the other, and the triangles of the "debris" are shown along the border and the wall lines. If it is listes below the other, it is covered by the "water", and the triangles of the "debris" are shown only along the "border" lines

For the lines the "context" option seems to change the type of the line. For example a line of type border with a -context line overhang" is drawn as a line of type overhang.

The same thing happes for the points. A point of type "moonmilk" with "-context point entrance" is drawn with the entrance symbol. There are exceptions: a point of type "label" is always written with the text of the label.

Areas cannot have "holes" inside that are not made of bedrock, ie, it is not possible to make an area with the shape of a donut, unless the hole inside the area is bordered by a "wall" line (with "-outline in").

If you need to create an area with a hole bordered by a line that does not contribute to the scrap outline, you can place another area, of type "bedrock", that covers the hole. This "hole" area must come before the area with hole in the list of commands, because therion stacks these (for the Metapost processing) from the end, and the "hole" area must cover the other one.

Some PDF viewer do not handle correctly transparency, and the hole still appear coloured, although differently. This is the case for xpdf and Preview (on Mac).

You can avoid areas with holes by joining the interior border to the exterior one with an invisible (option "-visibility off") border line, and draw the contour of the area that spans the exterior border, the invisible line, the interior border, and the invisible line again. The figure below shows the areaof of a pond with a rock boulder in the middle.

Area types
Area with hole
Area on two scraps