5.3　Field Selection of Routing Scheme

5.3.1　When selecting the routing scheme in the field，the surveyors shall verify the presence of national control points along the route and their distribution.

5.3.2　Where the routing scheme of the preliminary design stage deviates greatly from that of the feasibility study stage，supplementary reconnaissance，surveying and mapping shall be conducted，during which emphasis shall be put on planning areas，areas on which relevant agreements are reached，crowded areas，forests，areas with complicated construction conditions，important crossing-over，as well as areas where the transmission lines are parallel adjacent to communication lines.

5.3.3　Where the transmission lines run through or approach planning areas or areas on which relevant agreements are reached，and uniform plane coordinate systems are required，connection survey of plane coordinates shall be carried out.

5.3.4　Where a crowded area may affect the establishment of route，the plan of the crowded area shall be mapped with the scale of no less than 1∶5000.

5.3.5　For transmission lines of 35kV and above which may affect the establishment of route，proper instruments shall be used to survey their locations，crossing-over points，as well as the heights of poles at both ends.

5.3.6　Where the lines impose effect on parallel adjacent communication lines on either side，annotation or survey shall be carried out，after which the survey results shall be indicated on the topographic maps or a relative position map of dangerous effects of communication lines shall be developed.When the approach distance is less than 100m，the scale of map should be 1∶10，000.

5.3.7　Where the transmission lines run through a river，lake or reservoir，the surveyors shall cooperate with the hydrological personnel in surveying the hydrological sections，gradients and flood marks if necessary.

5.3.8　When erecting a tower in the river or lake，the surveyors shall survey the underwater topography or section，and the scale of underwater topographic map shall not be less than 1∶2000.The methods and precision indicators for surveying the underwater topography shall comply with the relevant provisions of GB 50026 Code for Engineering Surveying.