Bridge and Tunnel Entrances 2023

Bridges: All bridges are digitized as polygons. Bridges carry roads or railroads over water. Outside edges of all bridges delineated. Also bridge deck locations or clear spans where deck is not visible. This includes all overpasses (bridges that carry traffic over roads or railroads) and underpasses. Outside edge of all overpasses delineated. Bridges overlap road polygons. Pedestrian bridges are not captured. Tunnel Entrances: Entire tunnels are not captured, but all entrances to a tunnel are captured as polygons illustrating the width of the tunnel. Polygons plotted around tunnel openings and any abutments or walls which identify the tunnel entrance. Hidden Bridges: Hidden bridges are features that run under other features such as other bridges, overpasses, or tunnels and are not fully visible in an aerial photograph. The locations are interpreted based on the information visible on either side of the bridge.桥梁类：所有桥梁均以多边形（polygon）要素进行数字化表达。桥梁用于跨越水体并承载道路或铁路通行。已勾勒所有桥梁的外边缘；对于桥面不可见的区段，亦标注桥面位置或净跨径。本数据集涵盖所有跨线桥（overpass，即承载交通跨越道路或铁路的桥梁）及下穿桥（underpass），并勾勒所有跨线桥的外边缘。桥梁多边形会与道路多边形产生空间重叠。人行天桥未被纳入采集范围。 隧道入口类：未采集完整隧道主体，但所有隧道入口均以多边形要素采集，用于体现隧道的宽度。多边形将围绕隧道洞口及用于标识隧道入口的桥台或墙体绘制。 隐蔽桥梁类：隐蔽桥梁是指位于其他地物（如其他桥梁、跨线桥或隧道）下方，在航空影像中无法完全显现的地物。其位置将结合桥梁两侧可见的影像信息进行解译判定。