A control survey design should take into account: (1) the number and physical location of project points (i.e., distribution and geometry); (2) the standard errors you expect to achieve from field measurements; and (3) the number and types of observations to be measured (repeat measurements and instrument types). With these variables, especially the first two, a presurvey analysis may be carried out (e.g., by using least squares propagation) to assess the best design alternative (Section 6.4.4).