When it is necessary to design a building for a site that is not level, the architect must know just how high each point is above the lowest part of the site. This information is obtained by the surveyor and presented in a manner similar to that shown on Plate 31, which without the building, is called a contour map.
By way of an explanation of this map, imagine a flooded condition of the neighborhood in which the water is gradually rising. The part of the lot first covered by the water would be that at the corner of Salem Avenue and North Harvard Boulevard. Here the shore line would follow the dotted line figured 101. After the water had risen 4 feet more the shore line would follow the dotted line 105 and the water would have almost reached the location of the building. Thus it will be seen that each dotted line represents points of the same level across the lot.
Notice on the curb near the street intersection the bench mark which is figured 100. This is always established on some fixed object and the various levels measured from it by means of an instrument called a surveyor's level.
Notice now the note on the plan of the building which says that the basement floor elevation is 105.0. This means that the basement floor is to be 5' - 0" above the bench mark. Thus all levels of the building and site are measured from this fixed elevation.
The contour map is valuable in that it tells the architect (after he has located the building upon it) just how far below the first floor the ground is at any point around the building. This information is necessary in the placing of doorways, windows, steps, etc., in the outside wall at the ground level. It is also useful in determining the amount of excavating which must be done for the basement, and the fill for grading outside, when the building has been completed.
The given site plan shows also the location of the existing trees and their approximate size. They are indicated by the spots on the drawing and are sometimes noted as to kind and size.
Location and depth of sewers and location of the water main are also shown.
The points of the compass are given on the map when they are needed.
The lines showing the original contour of the lot are shown on this map by dotted lines and the future or proposed grade is shown by solid freehand lines.
Dimensions of the lot and location of the building on it are also given.
The opposite plan of the Grace Methodist Church which is called a general floor plan, has been given to illustrate the method of laying out an irregular building and to show the indication of stone, brick, structural tile and wood on a plan.
It should be noticed first that everything has been located from the central point near the change in direction of the plan and that all main dimensions are given to center lines radiating from this point.
Nothing can or need be shown in detail at this small scale, each door, window, etc., being represented by a symbol and detailed at a larger scale on other drawings.
The large letters in the circles are not a part of the drawing but will be referred to when studying Plate 34.