Cook_County_GISHydrographic data was collected for all of Cook County. Significant flowing and standing water features that were visible on the aerial photography were stereocompiled from 1998 aerial photography. The hydrographic midline data set represents, as a single line, the interpreted midline of flowing water features as seen on the aerial photography. The hydrographic midline data layer is used to show the location of the midline of natural drainage features, and is connected to polygonal (standing) hydrographic features such as lakes and ponds. The midline data layer also includes drainage features less than five feet in width, which were not included in the polygon hydrography data set. Midlines were added to water bodies such as double-line rivers to maintain the linear connectivity of the hydrographic network. Where the course of linear features (such as streams and rivers) in the hydrographic midline layer could not be compiled photogrammetrically due to being obscured by other features (such as vegetation or shadows), the obscured line segment was coded as "interpreted". In some cases, a flowing water feature may have run through an underground drain or culvert or its course otherwise obscured from view on the aerial photography. For such cases, in order to maintain linear connectivity of the features, its path was also interpreted and coded as such. Some hydrographic data was provided by the City of Chicago and incorporated into this data layer. These hydrographic data layers are modeled and stored as a network coverage containing polygons and/or lines. This midline data layer was created out of need by Cook County to develop a hydrographic layer in which water features are represented as single lines. The intended primary use of this data layer is for small-scale mapping and networking. The hydrographic midline layer was intersected with the street midline and railroad data layers to create nodes in the coverage model. It was also intersected with the bridge polygon data layer. Where hydrographic midline segments fall within a bridge polygon, they have been given a grade separation code of zero (0) to indicate the water level is technically "at grade". Hydrographic attributes include feature name, tax map name, and type. The primary source of the attribute information was the Cook County Highway Department database. Hydrographic names and alias IDs are linked to lookup tables based on the hydrographic name ID attribute.ArcGIS DynamicMapLayerhttps://hub.arcgis.com/datasets/caa697dac1944713bf5f9f7e17fdc0c5_6engCook CentralPublicStreams of Cook County [Illinois--Cook County]Web servicesIllinois--Cook CountyIllinoisLast Modified: 2022-09-14