Plate II
In hasty sketching, in order to save time, instead of using the regulation Conventional Signs, very often simply the outline of the object, such as a wood, a vineyard, a lake, etc., is indicated, with the name of the object written within the outline, thus:
Fig. 19
Such means are used very frequently in rapid sketching, on account of the time that they save.
By reference to the [map of Fort Leavenworth], the meaning of all its symbols is at once evident from the names printed thereon; for example, that of a city, woods, roads, streams, railroad, etc.; where no Conventional Sign is used on any area, it is to be understood that any growths thereon are not high enough to furnish any cover. As an exercise, pick out from the map the following conventional signs: Unimproved road, cemetery, railroad track, hedge, wire fence, orchard, streams, lake. The numbers on the various road crossings have no equivalent on the ground, but are placed on the maps to facilitate description of routes, etc. Often the numbers at road crossings on other maps denote the elevation of these points.
Visibility
[1875]. The problem of visibility is based on the relations of contours and map distances previously discussed, and includes such matters as the determination of whether a point can or can not be seen from another; whether a certain line of march is concealed from the enemy; whether a particular area is seen from a given point.