Practical: Showing relief with contour lines on maps
Contour lines join points of the same absolute height on a map. They show relief (hills, depressions, ravines). The height difference between neighbouring contours is the same (for example 10 or 20 m); it is chosen by map scale and how rugged the land is. A berg stroke is a short tick on a contour showing which way the slope goes down. On a hill the ticks point outward; in a depression they point inward. The closer together the contours are, the steeper the slope; the further apart, the gentler. Colouring the space between contours by height makes relief easier to read: low land green, then lighter and darker brown as height increases; water depth is shown by darker blue. Without ticks: if the inner contour has a bigger number than the outer one it is a hill; if smaller, a depression.
Model: make two cones from thick coloured paper (one steep, one gentle), cover them with plasticine and place both in a clear plastic box. Pour in 200 ml of water at a time and each time mark the water level on the cones with a marker. Looking from above, the marked lines are contours. On the steep cone the lines are closer together. Safety: do not spill water (slipping risk), do not put plasticine in the mouth, and wash hands afterwards.