Hydrography Subset Polygon includes the polygon features of a layer named Hydrography Subset. Hydrography Subset is a 1:24,000-scale, polygon and line feature-based layer that includes a prescribed set of hydrography features depicted on the U.S. Geological Survey (USGS) 7.5 minute topographic quadrangle maps for the State of Connecticut plus connecting lines that replace certain polygon features or bridge gaps in the hydrography in order to depict the hydrologic connections between upstream and downstream surface waterbodies. The hydrography features include perennial watercourses, waterbodies of at least 2.5 acres, dams, natural and manmade shorelines, ditches needed for connectivity, non-headwater intermittent streams, islands of at least 2.5 acres and stream connectors. Hydrography Subset is comprised of polygon and line features. Polygon features represent areas of water for rivers, streams, brooks, reservoirs, lakes, ponds, bays, coves, and harbors. Polygon features also depict dams and islands shown on the USGS 7.5 minute topographic quadrangle maps. Line features represent single-line rivers, streams, ditches, connectors replacing omitted ponds or marshes and connectors bridging gaps at underground watercourses. Line features also enclose all polygon features in the form of natural or manmade shorelines, dams, and closure lines separating adjacent waterbodies or forming the artificial end of a waterbody (data extent). The Hydrography Subset layer is based on information from USGS topographic quadrangle maps published between 1969 and 1984 so it does not depict conditions at any one particular point in time. Also, the layer does not reflect recent changes with the course of streams or location of shorelines impacted by natural events or changes in development since the time the USGS 7.5 minute topographic quadrangle maps were published. Attribute information is comprised of codes to identify hydrography features by type and describe feature area and length. The Hydrography Subset layer does not include bathymetric, stream gradient, water flow, water quality, or biological habitat information. The Hydrography Subset is not a hydrography network for modeling the direction of streamflow. This layer was originally published in 1994. The 2005 edition includes the same water features published in 1994, however some attribute information has been slightly modified and made easier to use. Also, the 2005 edition corrects previously undetected attribute coding errors.
In 2004, the State of Connecticut, Department of Environmental Protection developed an automated procedure to maintain feature topology and attribute integrity for the Hydrography Subset layer. Using ArcInfo Workstation 8.3 software, this automated procedure was developed to systematically maintain a set of related hydrography data for the State of Connecticut, Department of Environmental Protection. These automated procedures were developed using the Arc Macro Language (AML) scripting environment and are recorded in an AML file named MAKECOVER.AML for the hydrography category of data for the State of Connecticut, Department of Environmental Protection. The MAKECOVER.AML maintains the features and feature attribute data for the Hydrography, Hydrography Subset, Waterbody, Named Waterbody, and Named Waterbody Connectors layers. For additional information related to the original source of data from the U.S. Geological Survey, refer to the Data User Guides and Standards for 1:24,000-Scale Digital Line Graphs and Quadrangle Maps available from the U.S. Geological Survey, National Mapping Program.
Publication dates of the USGS 7.5 minute topographic quadrangle maps for the State of Connecticut through 1984.
Hydrography as polygon features
Internal feature number. (Source: ESRI)
Feature geometry. (Source: ESRI)
Hydrography Subset Polygon Code. Numeric values that identify hydrography subset polygon feature types. (Source: State of Connecticut, Department of Environmental Protection)
| Value | Definition |
|---|---|
| 0 | Not Hydrography |
| 116 | Open Water, Bay, Estuary, Gulf, Ocean |
| 121 | Island (2.5 acres or larger) |
| 406 | Dam or Weir |
| 412 | Stream, River or Brook |
| 414 | Ditch or Canal |
| 421 | Lake or Pond (2.5 acres or larger) |
Hydrography Subset Polygon Type. Text values that correspond to the HSPOLY_COD attribute values. HYSUB_POLY is the English language of (decodes) the HSPOLY_COD field. (Source: State of Connecticut, Department of Environmental Protection)
Internet Mapping Software Legend. Text field for classifying and symbolizing hydrography line feature types in a simple manner for an Internet map. (Source: State of Connecticut, Department of Environmental Protection)
| Value | Definition |
|---|---|
| No Show | This category includes HSPOLY_COD 0 and 121 |
| Dam | This category includes HSPOLY_COD 406 |
| Water | This category includes HSPOLY_COD 116, 412, 414 and 421 |
Calculated area of a polygon feature in acres. Note, ACREAGE values are not automatically updated after modifying feature geometry (shape). Values must be recalculated after features are edited, simplified, clipped, dissolved, etc. (Source: State of Connecticut, Department of Environmental Protection)
Feature geometry. (Source: ESRI)
ArcView Legend. Text field for classifying and symbolizing hydrography line feature types on a map. (Source: State of Connecticut, Department of Environmental Protection)
| Value | Definition |
|---|---|
| No Show | This category includes HSPOLY_COD 0 and 121 |
| Dam | This category includes HSPOLY_COD 406 |
| Water | This category includes HSPOLY_COD 116, 412, 414 and 421 |
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Hydrography Subset is 1:24,000-scale base map data for use where the connectivity of surface water is important or where the complexity of the full detail of the 1:24,000-scale Hydrography layer is not desired. The original intent of this layer was to make a lighter-weight version of hydrography available to users at a time when a personal computer's resources were often limited and the full hydrography did not contain attributes such as waterbody names that could be used to reduce the size of the dataset through querying. An enduring benefit comes from the stream connectivity introduced by the addition of line connectors that replace certain polygon features. The Hydrography Subset depicts a prescribed set of the hydrography information published on the USGS topographic quadrangle maps. For base map purposes, use this layer with other 1:24,000-scale base map data such as Roads and Trails, Railroads, Airports, and Towns. The connectors in this layer may be used as a possible data source for other 1:24,000-scale layers with features that must coincide and line up with stream and shoreline features published on the USGS topographic quadrangle maps. The Hydrography Subset layer is not intended for maps printed at map scales greater or more detailed than 1:24,000 scale (1 inch = 2,000 feet.)
Polygon and line features that define portions of open water features such as rivers, streams, brooks, reservoirs, lakes,, ponds, bays, harbors, and coves were used. Other related features such as marsh areas, aqueducts and the majority of ditches, canals or intermittent watercourses were not incorporated into the Hydrography Subset. The Hydrography is in ArcInfo Coverage format.
This data source is a set of Mylar overlays delineating all rivers, streams, brooks, reservoirs, lakes, and ponds that appear on the 1:24,000-scale 7.5 minute topographic quadrangle maps published by the USGS for Connecticut. This data set contains lines representing the connectivity of water features. The Named Streams, Lakes and Ponds Mylars were originally compiled and mapped by James Bogar, a Cartographer with the State of Connecticut, Department of Environmental Protection.
Various editions of Hydrography Subset are identified as both a Source Used and a Source Produced during the Process Steps. The Hydrography Subset is in ArcInfo Coverage format.
Includes all polygon features from the Hydrography Subset where the AV_LEGEND attribute was not equal to a value of "No Show" (AV_LEGEND <> "No Show"). This criterion only includes true hydrography features and excludes secondary polygon features from the ArcInfo coverage that represent areas of land completely enclosed by water features. The Hydrography_Subset_Poly.shp is in Shapefile format.
Replacement of polygon features by line features - An ArcInfo Macro Language (AML) script was developed to programatically select ponds less than 2.5 acres in size that are found along the course of streams and replace them with line connector features. All ponds less than 2.5 acres in size and their dams were deleted. The pond connectors were checked visually on-screen and vertices were added to keep the shape of the connector within the bounds of the original pond feature. The connectors to replace marsh features or to bridge gaps in the original hydrography where a watercourse was not delineated were digitized on-screen while visually referencing the Streams, Lakes and Ponds Mylar manuscripts as a guide. Each of the three types of connectors (stream connector replacing omitted pond, stream connector replacing omitted marsh, stream connector replacing omitted misc feature) was assigned its own HSARC_COD attribute value.
Attribute value reclassification - Feature codes in HSARC_COD and HSPOLY_COD were simplified by reclassifying certain features to a more general code. For example a siphon became a stream, a cranberry bog became a pond, a spillway or canal lock became a dam.
Final processing - Line features were unsplit based on the HSARC_COD attribute field to reduce the number of line feature records. Line features were not generalized (smoothed) and retain the original shape inherited from the Hydrography layer. Final visual inspection, editing and cleaning was done to assure connectivity and enforce line and polygon topology rules. The Hydrography Subset was created from the Hydrography layer before stream and lake names were assigned to the individual Hydrography features, therefore, no waterbody name attributes exist in the subset.
Datum conversion - Using ESRI ArcInfo software, the Hydrography layer was converted from the Connecticut State Plane Coordinate System of 1927 (NAD27) to the Connecticut State Plane Coordinate System of 1983 (NAD83). The NADCON (North American Datum CONversion) data transformation was used.
Attribute enhancements - AV_LEGEND, HYSUB_POLY and HYSUB_ARC attributes were changed from storing abbreviated values in upper case (e.g. STREAM) to full length values in both upper and lower case (e.g. Stream). Additionally, the IMS_LEGEND attribute was added to establish a very general classification scheme for symbolizing hydrography features with Internet mapping software environments such as ArcIMS.
Waterbody attribute enhancements - Previously undetected attribute value errors with HSARC_COD and HSPOLY_COD attribute values were corrected. Using Arc Macro Language (AML), an automated process (MAKECOVER.AML) was developed to maintain consistent attribute values by programmatically joining lookup data tables to decode numeric code fields and basing certain attribute information on polygon and line feature topology relationships.
Export to Shapefile Format - Converted data from ArcInfo Coverage to Shapefile format and named the shapefile Hydrography_Subset_Poly.shp. Excluded the AREA, PERIMETER, HYDRO#, HYDRO-ID attributes from the Shapefile because their values are only maintained by ArcInfo software with data that is in ArcInfo Coverage format. Includes all polygon features from the Hydrography Subset where the AV_LEGEND attribute was not equal to a value of "No Show" (AV_LEGEND <> "No Show"). This criterion only includes true hydrography features and excludes secondary polygon features from the ArcInfo coverage that represent areas of land completely enclosed by water features.
The Hydrography Subset layer attributes are based on the feature types identified by the USGS. All attributes have valid values. Values are within defined domains. The accuracy of the HSARC_COD and HSPOLY_COD attribute values is inherited from the Hydrography data. The attributes were generalized by computer reassignment of code values based upon table joins to lookup tables to aggregate similar types of features. The HYSUB_ARC, HYSUB_POLY, AV_LEGEND, and IMS_LEGEND attribute values are based on HSARC_COD and HSPOLY_COD values. HYSUB_POLY is the English language equivalent of (decodes) the HSPOLY_COD field for polygon features. HYSUB_ARC is the English language equivalent of (decodes) the HSARC_COD field for line features. AV_LEGEND and IMS_LEGEND are broad classifications of HSPOLY_COD and HSARC_COD values for polygon and line features, respectively. Based on the HSPOLY_COD and HSARC_COD attribute values, the HYSUB_POLY, HYSUB_ARC, AV_LEGEND, and IMS_LEGEND fields were populated through table joins to lookup tables. These decode values were not manually entered. The ACREAGE (area in acres) field was automatically calculated for each polygon feature based on computer generated feature area in square feet. The LENGTH_MI (length in miles) field was automatically calculated for each line feature base on computer generated feature length in feet.
This data complies with United States National Map Accuracy Standards for 1:24,000 scale maps regarding the features selected from the Hydrography layer. According to this standard, not more than 10 percent of the points tested are to be in error by more than 1/50 inch (40 feet) measured on the publication scale of a USGS 7.5 minute topographic quadrangle map. The connectors added to the Hydrography Subset layer begin and end at established hydrography features. The connectors represent an assumed path between connected features and not necessarily an actual path.
The Hydrography Subset is a set of hydrography features selected from the Hydrography layer according to certain rules and is, therefore, not a complete set of hydrography features. The completeness of the Hydrography data reflects the USGS National Mapping Division standards for feature content of the data sources, which are the Large Scale (7.5 minute) Digital Line Graph (DLG) files available from the USGS. For Connecticut, the Large Scale DLG files used to create this layer are for the 1:24,000-scale topographic quadrangle maps published between 1969 and 1984. The Hydrography layer used as a source is complete in the sense that it accurately reflects the contents of the most recently published USGS topographic quadrangle maps available at the time the State of Connecticut, Department of Environmental Protection began creating the layer. More recent quadrangle maps have been published by the USGS since 1984; however, the State of Connecticut did not incorporate this information into the Hydrography Subset layer. So compared to the most recent set of topographic quadrangle maps available today, the Hydrography Subset layer is incomplete, and substantially incomplete when compared to waterbodies present today. This data is not updated.
Polygon features conform to the following topological rules. Polygons are single part. There are no duplicate polygons. Polygons do not self overlap. Polygons do not overlap other polygons. Polygons are bound by lines. Line features conform to the following topological rules. Lines are single part. There are no duplicate lines. Lines do not self overlap. Lines do not overlap other lines. Lines intersect only at nodes, and nodes anchor the ends of all lines. Lines do not overshoot or undershoot other lines they are supposed to meet and intersect. The tests of logical consistency were performed by the State of Connecticut using ESRI ArcInfo software to maintain feature topology in ArcInfo coverage format. The data is topologically clean. The ArcInfo Clean function was repeatedly used following edits to verify topology and enforce a minimum distance between vertices of 4 feet (fuzzy tolerance) and a minimum allowed overshoot length of 10 feet (dangle length).
No restrictions or legal prerequisites for using the data. The data is suitable for use at appropriate scale, and is not intended for maps printed at scales greater or more detailed than 1:24,000 scale (1 inch = 2,000 feet). Although this data set has been used by the State of Connecticut, Department of Environmental Protection, no warranty, expressed or implied, is made by the State of Connecticut, Department of Environmental Protection as to the accuracy of the data and or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the State of Connecticut, Department of Environmental Protection in the use of these data or related materials. The user assumes the entire risk related to the use of these data. Once the data is distributed to the user, modifications made to the data by the user should be noted in the metadata. When printing this data on a map or using it in a software application, analysis, or report, please acknowledge the State of Connecticut, Department of Environmental Protection and the U.S. Geological Survey, National Mapping Program as the source for this information. For example, include the following data source description when printing this layer on a map: Hydrography - From the Hydrography Subset layer, compiled and published by CT DEP and USGS. Source map scale is 1:24,000.
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Although this data set has been used by the State of Connecticut, Department of Environmental Protection, no warranty, expressed or implied, is made by the State of Connecticut, Department of Environmental Protection as to the accuracy of the data and or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the State of Connecticut, Department of Environmental Protection in the use of these data or related materials. The user assumes the entire risk related to the use of these data. Once the data is distributed to the user, modifications made to the data by the user should be noted in the metadata.
| Data format: | in format Shapefile, Feature Class, ArcInfo Coverage (version ArcGIS) |
|---|---|
| Network links: | http://www.ct.gov/deep |
The data distributor does not provide custom GIS analysis or mapping services. Data is available in a standard format and may be converted to other formats, projections, coordinate systems, or selected for specific geographic regions by the party receiving the data.
79 Elm Street