很多年来，政府以及在某些情况下各个州已经对大量的各种用途的区域进行了测量。迄今为止，已经完成的主要工作包括确定了国家和州的边界线；绘出了海岸线和适于航行的河流和湖泊；精确定位了遍及全国的固定基准点；收集了遍布各个分散测站的关于地球磁力的有价值的论据；建立和观测了遍布世界的较大网络的重力站；建立和运转了潮位和水位站；扩充绘制了本来未绘制的约3/4的世界范围内与水文地理学和海洋学有关的图表和地图；扩充绘制了地球表面陆地的地形图。
Observations of a worldwide net of satellite triangulation stations（三角测量卫星观测站） were made during the decade 1964-1974. Results of the computations have been completed by 1985. They allow（有助于） determination of the shape of the earth from one to two orders of magnitude（数量级）better than has heretofore（迄今为止）been known. Consequently, surveys of global extent（全球范围）have been performed and will become common in the future.

在1964到1974年的十年间建立了全世界网络的三角测量的卫星观测站。到1985年已经完成了计算结果。它们有助于更精确地确定地球的形状，其精度要比迄今为止所知的高出一到两个数量级。因此，已经进行了全球范围的测量，这在将来成为平常事。
Thus surveys are divided into three classes: (a) those for the primary purpose of establishing the boundaries of land, (b) those providing information necessary for the construction of public or private works, and (c) those of large extent and high precision conducted by the government and to some extent by the states. There is no hard and fast line of demarcation（严格的界线）between surveys of one class and those of another（不同类型） regarding the methods employed, results obtained, or the use of the data of the survey.

因此，测量被分为三类：（a）主要用于确定土地边界的测量；（b）为公共或私人工程的建造提供必要信息的测量；（c）由政府以及在某种程度上由州进行的大范围和高精度的测量。不同类型的测量在采用的方法、取得的成果或测量数据的使用方面没有严格的界线。
Different types of surveying undertake（承担）the tasks of three classes. Geodetic surveying（大地测量） is employed in the third class, which takes into account the true shape of the earth. Surveys making use of the principles of geodesy（测地学）are of high precision and generally extend（遍布）over large areas. Where the area involved is not great, as for a state, the required precision may be obtained by assuming that the earth is a perfect sphere（球体）. Where the area is large, as for a country, the true spheroidal（椭球体）shape of the earth is considered. Surveys of the latter character have been conducted primarily through the agencies of governments. In the United States such surveys have been conducted principally by the U.S. National Geodetic Survey. Geodetic surveys have also been conducted by the Great Lake Survey, the Mississippi River Commission, several boundary commissions, and others.
不同类型的测量承担着这三类任务。大地测量被用于第三类的任务，它考虑了地球的实际形状。利用测地学原理的测量具有很高的精度，且通常遍布很大的范围。对包含的范围不大如一个州时，则可通过假定地球完全是个球体可以得到所需的精度。对范围较大如一个国家时，则要考虑地球实际的椭球体形状。对后者特征的测量主要通过政府机构进行。在美国这样的测量主要由美国国家大地测量局进行。大地测量也已由大湖勘测局、密西西比河委员会、一些边界线委员会以及其他机构进行。
Though relatively few engineers and surveyors are employed full time in geodetic work（测量工作）, the data of the various geodetic surveys are of great importance in that they furnish（提供）precise points of reference to which the multitude of（大量）surveys of lower precision may be tied（连接）. For each state, a system of plane coordinates（平面坐标系统）has been devised（建立）, to which all points in the state can be referred without an error of more than one part in 10 000 in distance or direction arising from the difference （差异）between the reference surface and the actual mean surface of the earth.
尽管较少的工程师和测量员专职从事测量工作，但是各种大地测量的数据很重要，它们提供了精确的基准点，大量较低精度的测量可与其联测。每个州都已建立了一个平面坐标系统，州内各点均可以参考这一坐标系统，基准面与实际的地球平均面之差所引起的距离或方位的误差不会大于1/10000。
That type of surveying in which the mean surface of the earth is considered as a plane, or in which its spheroidal shape is neglected, is generally defined as plane surveying. With regard to horizontal distances and directions, a level line（水平线）is considered as mathematically straight, the direction of the plumb line（铅垂线）is considered to be same at all points within the limits of the survey, and angles are considered to be plane angles. By far（到目前为止）the greater number of all surveys are of（属于）this type. In general the surveys necessary for the works of human beings are plane survey. The shape of the earth must be taken into consideration only in surveys of precision covering（涉及）large areas.
认为地球的平均面是一个平面或忽略椭球体形状的测量通常定义为平面测量。关于水平距离和方向，水平线在数学意义上被认为是直的，铅垂线的方向在测量限制范围内的所有点上被认为是相同的，而角度被认为是平面角。到目前为止，大多数的测量都属于这种类型。通常对人类工程必需的测量是平面测量。地球的形状只在涉及大范围的精确测量时才被考虑。