Building Footprints 2005 (Tacoma)

This polygon representation of built rooftop features is intended for quick mapping and impervious surface documentation. This data is static and may not represent current conditions and will be different than other sources such as basemaps. Each building has an associated elevation value. Omissions have been found throughout dataset, especially in industrial areas. Breaks between streets and driveways are not consistent. Objects coded as Unclassified include swimming pools, tennis courts, playgrounds, running tracks, etc. An Impervious Surface definition from the City of Tacoma: A hard surface area that either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include, but are not limited to, roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater. Open, uncovered retention/detention facilities shall not be considered as impervious surfaces for purposes of determining whether the thresholds for application of minimum requirements are exceeded. Open, uncovered retention/detention facilities shall be considered impervious surfaces for purposes of runoff modeling. Also available for download as CAD. From Tacoma Fire Service Area and Narrows Airport Planimetrics from July 2005 Ortho Photos.本数据集以多边形矢量形式表示建筑屋顶要素，可用于快速制图与不透水面（Impervious Surface）特征建档。本数据集为静态数据，无法反映当前地表实际状况，且与底图等其他数据源存在差异。每栋建筑均关联有高程值。数据集全域均存在要素遗漏情况，尤以工业区为甚。街道与车道之间的边界划分并不统一。被编码为未分类（Unclassified）的地物包括游泳池、网球场、游乐场、跑道等。塔科马市对不透水面的定义为：在开发前的自然状态下，能够阻止或延缓水分渗入土壤层的硬质地表区域；或相较于开发前的自然状态，可使地表径流量更大、径流速率更快的硬质地表区域。常见的不透水面包括但不限于屋顶、人行道、露台、车道、停车场或储物区、混凝土或沥青铺装路面、碎石路、压实土方区域，以及会同样阻碍雨水自然下渗的油浸碎石路面（macadam）或其他类似硬质地表。在判断是否超出最低要求适用阈值时，露天无覆盖的滞留/调蓄设施不应被视作不透水面；而在进行径流模拟时，露天无覆盖的滞留/调蓄设施则应被视作不透水面。本数据集亦可通过CAD格式下载获取。本数据集源自2005年7月的正射影像，涵盖塔科马消防服务区与纳罗斯机场的平面测图数据。