Town Survey Marks (TSM)

A standard Town Survey Mark (TSM) comprises of a brass peg in concrete at a depth of at least 24cm underground. It is protected by a cast iron cover placed flush with the ground surface. TSMs form part of an integrated surveyed system of control points throughout South Africa. The TSM dataset comprises of approx. 10000 control points at regular intervals within the municipal boundary of the City of Cape Town. They are maintained on an ongoing basis with its mandate given by the Land Survey Act 8 of 1997, section 42(4)a. TSMs are installed and surveyed to highest possible accuracy standards, usually at sub centimeter level. Their locational co-ordinates are determined by network adjust methods and precise levelling. Co-ordinates are based on the South African Hartebeesthoek 94 Datum and the World Geodetic System 1984 (WGS84) as ellipsoidal reference. All spatial layers are served live from internal systems, an item's "Last Updated" or "Publish Date" refers to the Metadata only.标准城镇测量标志（Town Survey Mark, TSM）为埋设于地下至少24厘米深处的混凝土内嵌黄铜测桩，采用与地面齐平的铸铁护盖进行防护。城镇测量标志是南非全境一体化测量控制点体系的组成部分。本次TSM数据集涵盖开普敦市行政辖区内按固定间隔布设的约10000个控制点，其维护工作依据《1997年第8号土地测绘法》第42(4)a款持续推进。TSM的布设与测量均遵循最高精度标准，精度通常可达亚厘米级，其点位坐标通过网平差方法与精密水准测量解算确定。坐标以南非哈特比斯普特94基准面（South African Hartebeesthoek 94 Datum）与世界大地测量系统1984（World Geodetic System 1984, WGS84）作为椭球参考基准。所有空间图层均由内部系统实时提供，要素的"Last Updated"与"Publish Date"仅针对元数据而言。