Connecticut 20 FT Contours is line feature-based data representing ground elevation at 20 ft intervals for Connecticut. This information was obtained from the University of Connecticut, College of Agriculture and Natural Resources and is a Beta product intended for research and demonstration purposes. The data is not consistently accurate statewide. In some areas there are anomalies with the contour line information due to data gaps in the underlying LiDAR data used to generate the contour lines. This is a known limitation of the LiDAR data collected for Connecticut in 2000. Areas where the contours are incorrect are typically easy to recognize because, in relation to nearby contours, they appear too straight and angular, do not naturally curve as expected, or don't exist where they probably should. Also, contour lines may not conform very well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to the anomalies in the data, use caution when viewing and analyzing this information. Attribute information consists of fields used to classify and label features based on 20 and 100 ft contour intervals.
Go to http://clear.uconn.edu for additional information on the LiDAR-derived data products generated from Connecticut's 2000 statewide LiDAR coverage.
collection date
20 FT ground elevation contours represented as line features (Source: State of Connecticut, Department of Environmental Protection)
Internal feature number. (Source: ESRI)
Feature geometry. (Source: ESRI)
Elevation of contour feature in feet (Source: Terrapoint LLC)
The type of contour line interval (e.g. 2, 10, 20, 50, and 100) based on the value of ELEVATION_FT. The larger interval - 100 instead of 50 for a 200 ft contour line - is assigned to a contour line. For example, a contour line interval value of 100 is assigned to features with ELEVATION_FT values of 100, 200, 300, 400, 500, etc. A contour line interval value of 50 is assigned to features with ELEVATION_FT values of 50, 150, 250, 350, 450, etc. A contour line interval value of 20 is assigned to features with ELEVATION_FT values of 20, 40, 60, 80, 120, etc. A contour line interval value of 10 is assigned to features having ELEVATION_FT values of 10, 30, 70, 90, 110, etc. A contour line interval value of 2 is assigned to features with ELEVATION_FT values of 2, 4, 6, 8, 12, 14, 18, etc. These values are used for querying subsets and classifying features for symbology purposes. For example, to make a 10 ft contour interval view of the data, query INTERVAL_FT IN (10, 20, 50, 100). To make a 20 ft contour interval view of the data, query INTERVAL_FT IN (20, 100). To make a 50 ft contour interval view of the data, query INTERVAL_FT IN (50, 100). To make a 100 ft contour interval view, query INTERVAL_FT IN (100). (Source: State of Connecticut, Department of Environmental Protection)
| Value | Definition |
|---|---|
| 20 |
20 foot contour interval |
| 100 |
100 foot contour interval |
20 FT Contour Label Field - An elevation value evenly divisable by 20. (Source: State of Connecticut, Department of Environmental Protection)
| Value | Definition |
|---|---|
| 20 |
20 ft label |
| 40 |
40 ft label |
| 60 |
60 ft label |
| 80 |
80 ft label |
| 100 |
100 ft label |
| etc. |
and so on |
100 FT Contour Label Field - An elevation value evenly divisable by 100. (Source: State of Connecticut, Department of Environmental Protection)
| Value | Definition |
|---|---|
| 100 |
100 ft label |
| 200 |
200 ft label |
| 300 |
300 ft label |
| 400 |
400 ft label |
| 500 |
500 ft label |
| etc. |
and so on |
Number assigned to USGS quadrangles that cover Connecticut. This information can help identify the original quarter-quarter quadrangle tile shapefile data source for an particular contour line. (Source: State of Connecticut, Department of Environmental Protection)
Length of feature in internal units. (Source: ESRI)
Includes 20 foot ground elevation contour line features. Information encoded about these features includes an ELEVATION_FT attribute and attributes for selection and cartographic symbology classification. Use the INTERVAL_FT attribute to select and symbolize features on a map. Use the ELEVATION_FT (for 2 foot contours), LABEL_10FT, LABEL_20FT, LABEL_50FT and LABEL_100FT attribute fields to label elevation values on a map. To define a layer that only includes 10 foot contour interval features, query LiDAR 2000 Contour features for INTERVAL_FT value equal to 10 or INTERVAL_FT value equal to 20 or INTERVAL_FT value equal to 50 or INTERVAL_FT value equal to 100. This selects the elevations that are divisible by 10. Similarly use INTERVAL_FT value equal to 20 or INTERVAL_FT value equal to 100 to select 20 foot contours, INTERVAL_FT value equal to 50 or INTERVAL_FT value equal to 100 to select 50 foot intervals, INTERVAL_FT value equal to 100 to select 100 foot intervals. The selected intervals can be used to cartographically represent the contour lines or add an elevation label to certain contour lines.
Aero-Metric, Inc. of Sheboygan Wisconsin was contracted by the State of Connecticut to provide the 2004 Statewide Aerial Survey of Connecticut. Contract deliverables include digital orthohotos, two sets of non-rectified prints for stereoscopic viewing, photo indexes, and LiDAR data. All 2004 Statewide Aerial Survey imagery and data products are defined under State of Connecticut contract award number RFP-990-A-14-0518-C (dated Feb 22, 2000), including contract award supplement #1 (dated Feb 28, 2002), contract award supplement #2 (dated Nov 4, 2004), contract award supplement #3 (dated Nov 26, 2004) and contract award supplement #4 (dated May 13, 2005). TerraPoint LLC of Woodlands Texas was subcontracted to create a Connecticut Statewide LIDAR dataset. Through funding by the Connecticut Joint Highway Research Council, project JH07-02, statewide LiDAR-derived datasets were subsequently created and made accessible by Associate Professor Thomas Meyer of the University of Connecticut, College of Agriculture and Natural Resources, Department of Natural Resources and the Environment. These derived data products include tiled point clouds, TINS, DEMs, and contour shapefiles available by USGS topographic quarter-quarter quadrangle area. CT DEP subsequently appended the statewide contour shapefiles into statewide datasets of 2, 10, 20, 50, and 100 foot intervals.
79 Elm Street
Connecticut 20 FT Contours are used to depict ground elevation at 20 ft intervals or greater. Each contour line represents a line of equal elevation and indicates surface relief when used with other information such as aerial photography, soils, geology, or hydrography.
These statewide line features of elevation contours were generated by UConn using point elevation data from the Connecticut Statewide LiDAR dataset. The Connecticut Statewide LiDAR dataset consists of x, y, and z point-data from an interpolated surface model ("bare-earth") derived from an Airborne LIDAR Topographic Mapping System (ALTMS). The x, y, and z values are stored in space-delimited ASCII files. These LiDAR elevation data are at a nominal 20-foot posting. The contours were prepared in one-sixteenth USGS quadrangle units. To understand the quad-sixteenth visualize a USGS quadrangle bisected vertically and horizontally into four sections. Each of these sections is in turn bisected vertically and horizontally into four sections, thus forming sixteen equal rectangles.
This data source refers to all features of quad-sixteenth contour shapefiles for each USGS quadrangle combined into one shapefile per quadrangle.
This data source is all the quadrangle contour shapefiles entered into an ESRI file geodatabase.
This is a statewide dataset that includes features from the individual quadrangle data sources. This dataset is in both File Geodatabase and ArcSDE feature class format. In ArcSDE, spatial views were created to establish 10, 20, 50, and 100 ft contour interval subsets, which were exported as the following File Geodatabase feature classes: LIDAR_2000_CONTOUR_10FT, LIDAR_2000_CONTOUR_20FT, LIDAR_2000_CONTOUR_50FT, and LIDAR_2000_CONTOUR_100FT.
Provided the polygon used to clip the contours to the state outline.
Provided the polygon to clip the contours along the Long Island Sound coastline.
Append shapefiles - Using ESRI ArcGIS software, append all quad-sixteenth contour shapefiles for each USGS quadrangle into a single shapefile for each quadrangle. A geoprocessing model able to append the shapefiles in batch was used. The lines in each quad were not dissolved. Tests showed that retaining the quad-sixteenth feature pattern helped create more uniform feature size. Tests also showed that dissolving would introduce an unacceptable number of errors into the data.
79 Elm Street
Load contours into geodatabase - Using ESRI ArcGIS software, create a file geodatabase and import the features in each appended contour shapefile into feature classes. During the import the attribute field named Value is renamed ELEVATION_FT. This field stores the elevation assigned to each contour line.
79 Elm Street
Clean up feature records - Using ESRI ArcGIS software, select all records in each contour feature class with a SHAPE_Length attribute of < .001 and delete. This removes features that are zero length lines and essentially are points. Using ESRI ArcGIS software, select all records in each contour feature class with an ELEVATION_FT of 0 or NULL and delete. This removes features that do not have a valid elevation assigned to them. The zero elevations contours occur over water bodies in about 30 quads with the highest concentrations occurring over Long Island Sound. These contour lines occur erratically and do not represent a base elevation.
79 Elm Street
Clean up features - Using ESRI ArcGIS software, select and delete small line features with the characteristics of length less than 100 feet and the beginning and ending point of the line are the same (small closed rings). Using a geoprocessing model designed to use in batch, temporary attribute fields were added and calculated for the X coordinate start, X coordinate end, Y coordinate start, Y coordinate end. Select records where "XCoorStart = XCoorEnd and YCoorStart = YCoorEnd and shape_length <= 100" and delete. The rings fitting these criteria are roughly 32 feet in diameter and appear to be anomalies or too small to be significant. This eliminates a large number of features in each feature class that provide little or no benefit. Refer to the quad-based appended shapefiles to see complete feature set.
79 Elm Street
Clip contour feature classes - Using ESRI ArcGIS software, clip and remove contour lines that extend outside the boundary of the State of Connecticut. The State of Connecticut polygon on file at DEP was used to clip off the landward contours that extend outside the state boundary. No offset was used. Using ESRI ArcGIS software, clip and remove contour lines that extend into Long Island Sound and its bays and harbors. The Long Island Sound polygon from hydrography data on file at DEP was modified and used to clip off seaward extending contours. These contour lines often contain processing artifacts from the original contour generation and are not intended to capture the water's surface. The Long Island Sound polygon was prepared before use. It was buffered to reduce its size by 40 feet from the mainland shoreline and offshore islands. A visual inspection of the Long Island Sound polygon, the contour lines and the 2004 orthophotographs was done along all shorelines. The Long Island Sound polygon outline was manually reshaped to accommodate variations in the contours and the shoreline on the orthophotograph such that all contours extend at least 40 feet.
79 Elm Street
Attribute enhancements - Using ESRI ArcGIS software and geoprocessing models designed to use batch processing, edit attribute fields. Remove the temporay fields used in Process Step 4. The field named ID did not contain data and was deleted. A field named QUAD_NO was added to store the number of each parent quadrangle to make it possible to backtrack to contour quad sources after the data is stored as a single datalayer. A field named INTERVAL_FT was added to classify the contour lines with elevation value ranges useful for symbolizing or selection of features. This field was populated by first assigning every contour line the base interval of 2 ft. In succession, the elevation values that participate in 10 ft, 20 ft, 50 ft and 100 ft intervals were selected and assigned. To use an interval remember to select all the intervals divisible by (contain) the number you are interested in. For example, to select elevations every 20 feet you should select INTERVAL_FT = 20 and INTERVAL_FT = 100.
79 Elm Street
Using ESRI ArcCatalog software, created a File GeoDatabase line feature class to store all of the 2 ft contour data. The individual quadrangle-based contour line feature classes are appended into a single feature class that included all 2ft contours statewide.
79 Elm Street
The LiDAR 2000 Contours layer retains the feature types and information identified by the State of Connecticut, Department of Environmental Protection and obtained from the LiDAR 2000 contour shapefiles. All attributes have valid values. Values are within defined domains. ELEVATION_FT attribute values are inherited from the LiDAR 2000 contour shapefiles. Attribute INTERVAL_FT was populated through successive selections of ELEVATION_FT values based on calculations to select values for 10 foot, 20 foot, 50 foot and 100 foot intervals. Attributes for LABEL_10FT, LABEL_20FT, LABEL_50FT, LABEL_100FT were populated through calculations. Attribute QUAD_NO was populated by assigning the number of the USGS quadrangle that the contours are located within.
The horizontal positional accuracy of this data is not known. This data underwent automated processes to interpolate and create 2 foot elevation contours from the 20-foot posting LiDAR 2000 point data. The horizontal positional accuracy of the 20-foot posting LiDAR 2000 point data is approximately 3 feet on the ground. The data is not consistently accurate statewide. In some areas there are anomalies with the contour line information areas due to data gaps in the underlying LiDAR data used to generate the contour lines. This is a known limitation of the LiDAR data collected for Connecticut in 2000. Areas where the contours are incorrect are typically easy to recognize because, in relation to nearby contours, they appear too straight and angular, do not naturally curve as expected, or don't exist where they probably should. Also, contour lines may not conform very well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to the anomalies in the data, use caution when viewing and analyzing this information.
The data is not consistently accurate statewide. In some areas there are anomalies with the contour line information areas due to data gaps in the underlying LiDAR data used to generate the contour lines. This is a known limitation of the LiDAR data collected for Connecticut in 2000. Areas where the contours are incorrect are typically easy to recognize because, in relation to nearby contours, they appear too straight and angular, do not naturally curve as expected, or don't exist where they probably should. Also, contour lines may not conform very well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to the anomalies in the data, use caution when viewing and analyzing this information.
The completeness of the data reflects the feature content of the data sources, which include the LiDAR 2000 contour shapefiles and the LiDAR 2000 elevation points. The LiDAR 2000 Contours layer contains automatically generated contour lines that may contain errors or inconsistancies inherent in the automated process. The LiDAR 2000 Contours layer contains errors or inconsistancies related to errors inherent in the original LiDAR elevation data capture. There are no plans to update or correct these data.
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 not performed by CT DEP. No automated procedures or tests were performed by CT DEP to guarantee desired topology other than limited visual inspection.
None. No restrictions or legal prerequisites for using the data after access is granted. The data is suitable for use at appropriate scale, however these data are not consistently accurate statewide. In some areas there are anomalies with the contour line information due to data gaps in the underlying LiDAR data used to generate the contour lines. This is a known limitation of the LiDAR data collected for Connecticut in 2000. Areas where the contours are incorrect are typically easy to recognize because, in relation to nearby contours, they appear too straight and angular, do not naturally curve as expected, or don't exist where they probably should. Also, contour lines may not conform very well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to the anomalies in the data, use caution when viewing and analyzing this information. 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 as the source for this information.
79 Elm Street
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 File Geodatabase (version ArcGIS 9) Size: 0.057
|
|---|---|
| Network links: | http://www.ct.gov/dep |
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