Connecticut 5 ft Contours (Revised) is line feature-based data representing ground elevation at 5 foot intervals for the state of Connecticut. This data replaces the 5 ft contour data previously available from CT DEP. It has fewer errors and data gaps than the previously available contours; however, some inaccuracies remain. These contour lines have been processed to appear smoother and less jagged than the previous data and have been optimized for faster drawing and performance. The source for these data is the Connecticut LiDAR 10-foot DEM (file name: ct_lidar) from the Center for Land Use Education and Research at the University of Connecticut, College of Agriculture and Natural Resources.
Connecticut 5 ft Contours (Revised) is used to depict ground elevation at 5 foot 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.
ground condition
The data is suitable for use at appropriate scale; however, these data are not consistently accurate statewide. Users should review the following description of source data and process steps in order to determine the appropriate uses of this information. The original data source was 20-foot posting LiDAR point data collected in 2000, which has a horizontal positional accuracy of approximately 3 feet on the ground. The LiDAR point data has known limitations including data gaps. While the contour lines previously available from CT DEP were derived directly from the LiDAR point data, these contour lines were derived from the Connecticut LiDAR 10-foot DEM (file name: ct_lidar) from the Center for Land Use Education and Research (CLEAR) at the University of Connecticut, College of Agriculture and Natural Resources. During the production of the Connecticut LiDAR 10-foot DEM, CLEAR manually edited the data to fill in data gaps with coarser data based on contour lines from USGS topographic maps. Therefore, these contour lines contain fewer errors than the previously available contour lines. In order to produce less jagged contour lines, a circular averaging filter with a radius of 3 cells was applied to the Connecticut LiDAR 10-foot DEM (file name: ct_lidar). The contour lines were produced from this smoothed DEM. Visual inspection has shown that the resulting contour lines align well with the contour lines previously available from CT DEP. These contour lines, while less error-prone than the previous data, retain some errors from the LiDAR point data and may have other errors introduced during the editing and processing steps. Contour lines may not conform well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to these anomalies, use caution when viewing and analyzing this information. There are no restrictions or legal prerequisites for using the data after access is granted. 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 Conneticut, 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 these 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.
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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. The University of Connecticut, College of Agriculture and Natural Resources subsequently created and made accessible a variety of LiDAR-derived datasets. One of these, the Connecticut LiDAR 10-foot DEM (file name: ct_lidar), was used to create the smoothed statewide DEM from which this revised contour line feature class was created.
Connecticut 5 ft Contours (Revised) retains the feature types and information identified by the State of Connecticut, Department of Environmental Protection and derived from the Connecticut LiDAR 10-foot DEM. All attributes have valid values. Values are within defined domains. ELEV_FT attribute values are derived from the Connecticut LiDAR Smoothed DEM. Attribute INT_FT was populated through successive selections of ELEV_FT values based on calculations to select values for 5, 10, 20, and 50 foot intervals. Attributes for LABEL_5, LABEL_10, LABEL_20, and LABEL_50 were populated through calculations. Attributes QUAD_NO and QUAD_NAME were populated by assigning the number and name of the USGS quadrangle that the contours are located within.
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.
The completeness of the data reflects the content of the data sources, which consists of the Connecticut LiDAR 10-foot DEM (file name: ct_lidar) and its sources, the LiDAR 2000 elevation points and USGS topograhic maps. This data contains automatically generated contour lines that may contain errors or inconsistencies inherent in the automated process. The data also contains errors or inconsistencies related to errors inherent in the original LiDAR elevation data capture. There are no plans to update or correct these data.
The horizontal positional accuracy of this data is not known. Users should review the following description of source data and process steps in order to determine the appropriate uses of this information. The original data source was 20-foot posting LiDAR point data collected in 2000, which has a horizontal positional accuracy of approximately 3 feet on the ground. The LiDAR point data has known limitations including data gaps. While the contour lines previously available from CT DEP were derived directly from the LiDAR point data, these contour lines were derived from the Connecticut LiDAR 10-foot DEM (file name: ct_lidar) from the Center for Land Use Education and Research (CLEAR) at the University of Connecticut, College of Agriculture and Natural Resources. During the production of the Connecticut LiDAR 10-foot DEM, CLEAR manually edited the data to fill in data gaps with coarser data based on contour lines from USGS topographic maps. Therefore, these contour lines contain fewer errors than the previously available contour lines. In order to produce less jagged contour lines, a circular averaging filter with a radius of 3 cells was applied to the Connecticut LiDAR 10-foot DEM (file name: ct_lidar). The contour lines were produced from this smoothed DEM. Visual inspection has shown that the resulting contour lines align well with the contour lines previously available from CT DEP. These contour lines, while less error-prone than the previous data, retain some errors from the LiDAR point data and may have other errors introduced during the editing and processing steps. Contour lines may not conform well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to these anomalies, use caution when viewing and analyzing this information.
The data is not consistently accurate statewide. These contour lines, while less error-prone than the previous data, retain some errors from the LiDAR point data and may have other errors introduced during the editing and processing steps. Contour lines may not conform well to the shoreline of waterbodies and in many instances erroneously extend into areas of water. Due to these anomalies, use caution when viewing and analyzing this information.
This statewide digital elevation model (DEM) was generated by the Center for Land Use Education and Research (CLEAR), University of Connecticut using the 2000 Connecticut LiDAR point dataset, which consists of bare-earth x, y, and z point data 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. To improve the DEM, CLEAR manually edited the 2000 Connecticut LiDAR point dataset to erase erroneous data and fill in data gaps with added points derived from contour lines that appear on USGS 1:24,000-scale Digital Raster Graphics (DRGs).
This data source contains the USGS quadrangles that cover the state of Connecticut. It was used to divide the contour lines into more evenly distributed shape lengths and to add attribute information.
This data source is a smoothed version of the Connecticut LiDAR 10-foot DEM. The smoothing was performed using the ArcGIS Spatial Analyst extension to calculate a focal mean using a circular neighborhood with a radius of 3 cells.
The Connecticut Waterbody Polygon layer was used to sytematically select and remove contour lines that were contained completely within waterbody polygons.
Pre-processing the DEM: The Connecticut LiDAR 10-foot DEM was smoothed using the focal statistics tool in the ArcGIS Spatial Analyst extension. A circular neighborhood with a radius of 3 cells was used, and the statistic calculated was the mean.
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Generate contours: The ArcGIS 3D Analyst extension was used to create four contour feature classes from the smoothed DEM at 20-foot intervals, using a different base contour value for each. The base contour values were 0, 5, 10, and 15. The first feature class has a base contour value of 0 and contains the contour values 20, 40, 60, etc; the second feature class has a base contour value of 5 and contains contour values 5, 25, 45, etc; and so forth. The process was done in this way after attempts to produce 5 foot contours for the entire state failed because there was insufficient processing capacity to generate them all at once.
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Optimize contours: The line features were simplified by removing redundant vertices using the Simplify Line tool in ArcGIS. For the 5 foot contours, the maximum allowable offset was set to 2 feet. In testing, this offset value improved the performance of the feature class without making a significant visual difference when viewed at an appropriate scale.
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Clean up records: Self-intersecting line features with a shape length of less than 25 feet were sytematically selected and removed. These features were circular contours so small they appeared almost as points when viewed at an appropriate scale. Therefore, they were determined to be too small to provide meaningful information. Subsequently, features that were completely within a waterbody polygon were sytematically selected and removed.
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Edit attributes: The ArcGIS Identity tool was used to add USGS quadrangle attributes and to break up features into more uniform lengths for drawing and labeling performance purposes. The ID attribute was removed as it did not contain meaningful information. The Contour field was renamed ELEV_FT. The INT_FT attribute was added to classify the contour lines with elevation value ranges useful for symbolizing or selection of features. Label fields were added to assist with labeling at different intervals.
Merge contours: the four 20-ft contour layers (with base contour values of 0, 5, 10, and 15) were merged together to create a statewide 5 foot contour layer.
Internal feature number.
ESRI
Feature geometry.
ESRI
Elevation of contour feature in feet
Terrapoint LLC / University of Connecticut, College of Agriculture and Natural Resources
The contour line interval in feet. This is based on the value of ELEV_FT. These values are used for querying subsets and classifying features for symbology purposes.
State of Connecticut, Department of Environmental Protection
5 foot contour interval
10 foot contour interval
20 foot contour interval
50 foot contour interval
5 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 5.
State of Connecticut, Department of Environmental Protection
10 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 10.
State of Connecticut, Department of Environmental Protection
20 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 20.
State of Connecticut, Department of Environmental Protection
50 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 50.
State of Connecticut, Department of Environmental Protection
Name assigned to USGS quadrangles that cover Connecticut.
State of Connecticut, Department of Environmental Protection
Feature geometry.
ESRI
Number assigned to USGS quadrangles that cover Connecticut
State of Connecticut, Department of Environmental Protection
Includes 5 foot ground elevation contour line features. Information encoded about these features includes an ELEV_FT attribute and attributes for selection and cartographic symbology classification. Use the INT_FT attribute to select and symbolize features on a map. Use the LABEL_5, LABEL_10, LABEL_20, and LABEL_50 attribute fields to label elevation values on a map.
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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.
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.
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