28 
In order to attain accuracy, continuity, and permanency in highway sur- 
veys, and to save time and money, it is advisable to make an adjustment in the 
plane coordinates of station markers in the basic network of control surveys 
that will be used as origin and closure points in basic control surveys for 
the project. This adjustment is made before project control surveys and map- 
ping are undertaken. The adjustments are made so that the plane coordinates 
Will apply at the mean elevation of the survey project. Then distances deter- 
mined therefrom will agree, within practicable limits of accuracy and without 
need for any correction, with distances measured horizontally on the ground 
between the points. An applicable combined adjustment factor, which includes 
both scale corrections and elevation corrections, is easily computed for any 
project by procedures outlined in the following paragraphs. 
For computing the applicable combined adjustment factor, an appropriate 
Scale correction factor (S.C.F.) is selected from the applicable State Plane 
Coordinate Projection Tables. The scale correction factor is the ratio of 
distances on datum of the State plane coordinate system to distances on mean 
sea level arc of the earth. Selection is made on the basis of scale correc- 
tion factor applicable at the mean latitude of the survey project where the 
State plane coordinates are based on a Lambert conformal projection, or on 
the basis of the mean X (East) coordinate of the survey project where the State 
plane coordinates are based on a Transverse Mercator projection. One factor 
only is used, unless the survey project is especially long. Under the latter 
circumstances if the project extends principally in a north-south direction in 
a Lambert zone, or in an east-west direction in a Transverse Mercator zone, the 
project is divided into segments so as to utilize an appropriate factor for 
each segment. 
The elevation multiplication factor (E.M.F.) is computed by ascertaining 
the elevation for datum of project plane coordinates half way between the low 
and high elevations, or the elevation levels for separate segments of the pro- 
Ject which are not more, respectively, than: 
l. 1,000 feet above low point and 1,000 feet below high point within the 
project segment, if an accuracy of not less than 1:10,000 is to be achieved, or 
2. 2,000 feet above low point and 2,000 feet below high point within the 
project segment, if an accuracy of not less than 1:5,000 is to be achieved. 
The elevation multiplication factor is equal to the addition of 1 to the pro- 
duct of h.70 x 1079 times the elevation at which the datum plane is estab- 
lished for the plane coordinates of the project, or segment of project. 
The combined adjustment factor (C.A.F.) 1s computed by dividing the E.M.F. 
by the S.C.F. and using six significant figures to the right of the decimal 
point. Then the State plane coordinates, X and Y (Fast and North) of each 
horizontal control point which will be used from the basic network is multi- 
plied by the C.A.F. The project plane coordinates thus determined for such 
points are used in computing closures in all basic control surveys made for 
control of project mapping. When State plane coordinates are required for 
any point in the project control surveys or on the maps controlled thereby, 
they are computed by dividing the project plane coordinates of the point by 
the combined adjustment factor: 
Topographic maps compiled by Stereophotogrammetric methods 
Materials for the base of map manuscripts are scale stable and durable. 
The size of the manuscripts is varied for convenience and suitability accord- 
ing to the purposes for which they are to be used. The scale of the manu- 
scripts is the same as or larger than required in the finished maps, except 
where limitations caused by the relief height to flight height ratio, in areas 
where buildings are tall and/or topography is rugged, make it necessary to com- 
pile maps at a scale smaller than required in the finished maps. Refer to 
table 5 for explicit details regarding the relief height to flight height ratio. 
The interval at which contours are delineated on the manuscripts is the same as 
required on the finished maps.