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Principal Meridian
Base Line
Standard Parallels
Guide Meridians

Manual of Instructions for the Survey of the Public Lands of the United States


3-8. A principal meridian is intended to conform to the true meridian, extending north or south, or in both directions, from the initial point as conditions require. Regular quarter-section and section corners are established alternately at intervals of 40 chains, and regular township corners at intervals of 480 chains. Corners designated as meander corners are established at the intersection of the line with meanderable bodies of water.

3-9. In the survey of the principal meridian and other standard lines (base lines, standard parallels, and guide meridians), two independent sets of measurements are made, but only the mean of the two measurements is shown in the final field notes. Double measurement may be omitted if subdivisional closings are provided in the same assignment with the standard line, in which case the closings furnish a verification of the length.

Should the difference between the two sets of measurements of a standard line exceed 7 links per 80 chains, the line is remeasured to reduce the difference. Should independent tests of the alinement of a standard line indicate that the line has deflected more than 3 minutes from the true cardinal course, the line must be rerun. These are the maximum discrepancies allowable in new surveys.



3-10. The base line is extended east and west from the initial point on a true parallel of latitude. Standard quarter-section and section corners are established alternately at intervals of 40 chains and standard township corners at intervals of 480 chains. Meander corners are established where the line intersects meanderable bodies of water.

3-11. The manner of making the measurement of the base line and the accuracy of alinement and measurement are the same as required in the survey of the principal meridian. The determination of the alinement of the true latitude curve may be made by the solar method, the tangent method, or the secant method as conditions require. The detailed process is described in the field notes.



3-12. Standard parallels, which are also called correction lines, are extended east and west from the principal meridian, at intervals of 24 miles north and south of the base line, in the manner prescribed for the survey of the base line.

3-13. Where standard parallels previously have been placed at intervals of 30 or 36 miles, and present conditions require additional standard lines, an intermediate correction line is established to which a local name may be given, such as "Fifth Auxiliary Standard Parallel North," or "Cedar Creek Correction Line," run, in all respects, like a regular standard parallel.



3-14.Guide meridians are extended north from the base line, or standard parallels, at intervals of 24 miles east and west from the principal meridian, in the manner prescribed for running the principal meridian. The guide meridians are terminated at the points of their intersections with the standard parallels. The guide meridian is projected on the true meridian, and the fractional measurement is placed in the last half mile. At the true point of intersection of the guide meridian with the standard parallel a closing township corner is established. The parallel is retraced between the first standard corners east and west of the point for the closing corner, in order to determine the exact alinement of the line closed upon. The distance is measured and recorded to the nearest corner on the standard parallel.

3-15. When existing conditions require that guide meridians be run south from the base or correction lines, they are initiated at the theoretical point for the closing corner of the guide meridian, calculated on the basis of the survey of the line from south to north initiated at the proper standard township corner. At the theoretical point of intersection a closing township corner is established.

3-16. Where guide meridians have been placed at intervals exceeding the distance of 24 miles, and new governing lines are required, a new guide meridian is established, and a local name is assigned, such as "Twelfth Auxiliary Guide Meridian West," or "Grass Valley Guide Meridian." Auxiliary guide meridians are surveyed in all respects like regular guide meridians.

  Fig. 15.
FIGURE 15 Survey of quadrangles, each embracing 16 townships bounded by standard lines, showing the coordinate system of numbering townships

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