70 THE UNITED STATES GEOLOGICAL SURVEY. [bull. 227. 
detic coordinates of from 300 to 400 primary and secondary points per 
annum. The positions of all points in the Appalachian region from 
Maine to Alabama, those along the thirty-ninth parallel from the 
Atlantic to the Pacific, and those along the ninety-eighth meridian are 
now computed upon the United States standard datum. 
The office work of primary traverse consists in the reduction of all 
azimuth observations and the adjustment of the line between azimuth 
stations, and of the computation of between 7,000 and 8,000 latitudes 
and departures and of 1,000 geographic positions per annum. 
The results of primary triangulation and traverse are summarized 
and published at the close of each fiscal year in the form of a bulletin 
(Series F). 
The office work of level adjustment consists in the preparation of 
plates showing groups of level circuits by States, with an indication 
of the error of each circuit. Where a group of primary level lines 
connects with the precise-level net at several points the errors are cor- 
rected by distribution in proportion to mileage, after determining 
weighted values for the intermediate points; but a group of circuits 
extending from one point or circuit is treated by adjusting first the 
circuit in which the largest closure (within limits) occurs and then 
correcting the remaining closure errors of successive circuits in pro- 
portion to the mileage. This method answers all practical purposes. 
The vast amount of leveling data sent in from all parts of the United 
States by the numerous field parties would not admit of a treatment 
by the method of least squares. As showing the amount of this class of 
work, it may be stated that during the last fiscal year (1902-3), 29,160 
miles of levels were adjusted, correcting the elevations of 1,826 bench 
marks. 
The results are annually summarized and published in the form of 
a bulletin (Series F). 
PL VI shows the progress made in astronomic location and primary 
control to January 1, 1901. 
For publications on this subject see the Survey's list of publications 
Section of Inspection of Surveying and Mapping. 
Coincident with the reorganization of the topographic branch in 1903 
provision was made for the inspection of topographic surveying and 
mapping, to be carried on through consultation and collaboration with 
the section chiefs. To the chief of this new section was also given the 
direction of the preparation of such base maps as might be required 
for various purposes. The inspection of field work and the final draw- 
ing of the maps lie entirely outside of the duties of administration, 
are general in character, and consist chiefly in keeping in touch with 
the various topographers, criticising their expression of topographic 
