The drawing of tiles is controlled here.
The Mode allows the drawing mode to be selected. The different modes
are explained here.
Anchor sets how tiles bigger than 8x8 are anchored. In all drawing
modes, apart from Plot and Text, where the shape is drawn from
will be set as the anchor for the tile (try it with a large tile and drawing
a filled rectangle to see what I mean). However, this anchor point is reset
for each drawing operation. By checking the box this anchor will not be reset.
To illustrate this, try drawing some lines with large tiles with the anchor
off, then try again with the anchor on.
Note that larger tiles are drawn correctly, so that the flip commands (see
below) are honoured and the tile is still drawn correctly.
Zoom allows you to zoom into the map for easier editing. Note that zoom
level zero draws the tiles half sized, so that an overview of a map can be seen
a bit more easily.
Tile selects the tile to be used for drawing, and the start tile in the
sequential drawing mode.
Flip Horiz (only when editing non-rotational maps) means that the tiles
will be drawn horizontally flipped. Flip Vert does the same, but
vertically.