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Connecticut 2 ft Contours (Revised)

Frequently-asked questions:


What does this data set describe?

Title:
Connecticut 2 ft Contours (Revised)

Abstract:
Connecticut 2 ft Contours (Revised) is line feature-based data representing ground elevation at 2 foot intervals for the state of Connecticut. This data replaces the 2 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.

  1. How should this data set be cited?

    State of Connecticut, Department of Environmental Protection (editor and publisher), University of Connecticut, College of Agriculture and Natural Resources (compiler and editor), State of Connecticut, Department of Public Safety, State of Connecticut, Department of Transportation, Connecticut Joint Highway Research Council, 20110502, Connecticut 2 ft Contours (Revised): State of Connecticut, Department of Environmental Protection, Hartford, Connecticut, USA.

    Online links:
  2. What geographic area does the data set cover?

    Bounding coordinates:
    West: -73.742906
    East: -71.780655
    North: 42.053150
    South: 40.979730

  3. What does it look like?

    http://cteco.uconn.edu/metadata/dep/browsegraphic/contoursfullview100ft.gif (GIF)
    Full view of the 100 ft contours. This image is included to show the coverage area of the 2 ft contours, which is the same area as for the 100 ft contours.

    http://cteco.uconn.edu/metadata/dep/browsegraphic/contoursdetailview2ft.gif (GIF)
    Detail view of the 2 ft contours.

    http://cteco.uconn.edu/metadata/dep/browsegraphic/contoursdatagapbefore.gif (GIF)
    A data gap in the contour lines previously available from DEP

    http://cteco.uconn.edu/metadata/dep/browsegraphic/contoursdatagapafter.gif (GIF)
    The revised contour lines, in the same area where there was previously a data gap

  4. Does the data set describe conditions during a particular time period?

    Calendar date: 2000
    Currentness reference:
    ground condition

  5. What is the general form of this data set?

    Geospatial data presentation form: vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • String (1749467)

    2. What coordinate system is used to represent geographic features?

      The map projection used is Lambert Conformal Conic.

      Projection parameters:
      Lambert Conformal Conic
      Standard parallel: 41.200000
      Standard parallel: 41.866667
      Longitude of central meridian: -72.750000
      Latitude of projection origin: 40.833333
      False easting: 999999.999996
      False northing: 499999.999998

      Planar coordinates are encoded using coordinate pair.
      Abscissae (x-coordinates) are specified to the nearest 0.000328.
      Ordinates (y-coordinates) are specified to the nearest 0.000328.
      Planar coordinates are specified in survey feet.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

      Vertical coordinate system definition:
      Altitude system definition:
      Altitude datum name: North American Vertical Datum of 1988
      Altitude resolution: 1.000000
      Altitude distance units: feet
      Altitude encoding method: Explicit elevation coordinate included with horizontal coordinates

  7. How does the data set describe geographic features?

    Connecticut 2 ft Contours (Revised)
    2 ft ground elevation contours represented as line features (Source: State of Connecticut, Department of Environmental Protection)

    OBJECTID
    Internal feature number. (Source: ESRI)
                      

    Sequential unique whole numbers that are automatically generated.

    Shape
    Feature geometry. (Source: ESRI)
                      

    Coordinates defining the features.

    ELEV_FT
    Elevation of contour feature in feet (Source: Terrapoint LLC / University of Connecticut, College of Agriculture and Natural Resources)
                      

    Range of values
    Minimum:2
    Maximum:2412

    INT_FT
    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. (Source: State of Connecticut, Department of Environmental Protection)
                      

    ValueDefinition
    2
    2 foot contour interval
    10
    10 foot contour interval
    20
    20 foot contour interval

    LABEL_2
    2 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 2. (Source: State of Connecticut, Department of Environmental Protection)
                      

    Range of values
    Minimum:2
    Maximum:2412

    LABEL_10
    10 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 10. (Source: State of Connecticut, Department of Environmental Protection)
                      

    Range of values
    Minimum:10
    Maximum:2410

    LABEL_20
    20 foot contour label field. Used to label all contour lines with an elevation value evenly divisible by 20. (Source: State of Connecticut, Department of Environmental Protection)
                      

    Range of values
    Minimum:20
    Maximum:2400

    QUAD_NAME
    Name assigned to USGS quadrangles that cover Connecticut. (Source: State of Connecticut, Department of Environmental Protection)
                      

    USGS-assigned name

    SHAPE
    Feature geometry. (Source: ESRI)
                      

    Coordinates defining the features.

    QUAD_NO
    Number assigned to USGS quadrangles that cover Connecticut (Source: State of Connecticut, Department of Environmental Protection)
                      

    Integer

    SHAPE.len
    Entity and attribute overview:
    Includes 2 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_2, LABEL_10, and LABEL_20 attribute fields to label elevation values on a map.
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Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)


  2. Who also contributed to the data set?

    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.

  3. To whom should users address questions about the data?

    Howie Sternberg
    State of Connecticut, Department of Environmental Protection
    79 Elm Street
    Hartford, CT 06106-5127
    USA

    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time
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Why was the data set created?

Connecticut 2 ft Contours (Revised)  is used to depict ground elevation at 2 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.

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How was the data set created?

  1. Where did the data come from?

    10-foot DEM (source 1 of 4)

    University of Connecticut, College of Agriculture and Natural Resources, Unknown, Connecticut LiDAR 10-foot DEM (file name: ct_lidar): University of Connecticut, Center for Land Use Education and Research (CLEAR), Storrs, Connecticut, USA.

    Online links:
    Type of source media: disc
    Source contribution:
    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).

    USGS Quad Index (source 2 of 4)

    State of Connecticut, Department of Environmental Protection, 1985, Connecticut USGS 7.5 Minute Quadrangle Index: State of Connecticut, Department of Environmental Protection, Hartford, Connecticut, USA.

    Online links:
    Type of source media: disc
    Source scale denominator: 24000
    Source contribution:
    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.

    Smoothed DEM (source 3 of 4)

    State of Connecticut, Department of Environmental Protection, Unpublished Material, Connecticut LiDAR Smoothed DEM (file name: ct_dem_smooth).

    Type of source media: computer program
    Source contribution:
    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.

    Waterbodies (source 4 of 4)

    U.S. Geological Survey, National Mapping Program, 1999, Connecticut Waterbody Polygon: State of Connecticut, Department of Environmental Protection, Hartford, Connecticut, USA.

    Online links:
    Type of source media: disc
    Source scale denominator: 24000
    Source contribution:
    The Connecticut Waterbody Polygon layer was used to sytematically select and remove contour lines that were contained completely within waterbody polygons.

  2. What changes have been made?

    Date: 20110401 (change 1 of 6)
    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.

    Person responsible for change:
    Courtney Larson
    State of Connecticut, Department of Environmental Protection
    79 Elm Street
    Hartford, CT 06106-5127
    USA

    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

    Data sources used in this process:
    • 10-foot DEM

    Data sources produced in this process:
    • Smoothed DEM

    Date: 20110401 (change 2 of 6)
    Generate contours: The ArcGIS 3D Analyst extension was used to create ten 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, 2, 4, 6, 8, 10, 12, 14, 16, and 18. 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 2 and contains contour values 2, 22, 42, etc; and so forth. The process was done in this way after attempts to produce 2 foot contours for the entire state failed because there was insufficient processing capacity to generate them all at once.

    Person responsible for change:
    Courtney Larson
    State of Connecticut, Department of Environmental Protection
    79 Elm Street
    Hartford, CT 06106-5127
    USA

    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

    Data sources used in this process:
    • Smoothed DEM

    Data sources produced in this process:
    • Ten 20-ft contour layers

    Date: 20110401 (change 3 of 6)
    Optimize contours: The line features were simplified by removing redundant vertices using the Simplify Line tool in ArcGIS. For the 2 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.

    Person responsible for change:
    Courtney Larson
    State of Connecticut, Department of Environmental Protection
    79 Elm Street
    Hartford, CT 06106-5127
    USA

    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

    Data sources used in this process:
    • Ten 20-ft contour layers

    Data sources produced in this process:
    • Ten 20-ft contour layers

    Date: 20110401 (change 4 of 6)
    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.

    Person responsible for change:
    Courtney Larson
    State of Connecticut, Department of Environmental Protection
    79 Elm Street
    Hartford, CT 06106-5127
    USA

    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

    Data sources used in this process:
    • Ten 20-ft contour layers

    Data sources produced in this process:
    • Ten 20-ft contour layers

    Date: 20110401 (change 5 of 6)
    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.

    Person responsible for change:
    Courtney Larson
    State of Connecticut, Department of Environmental Protection
    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

    Data sources used in this process:
    • Ten 20-ft contour layers

    Data sources produced in this process:
    • Ten 20-ft contour layers

    Date: 20110401 (change 6 of 6)
    Merge contours: the ten 20-ft contour layers (with base contour values of 0, 2, 4, 6, 8, 10, 12, 14, 16, and 18) were merged together to create a statewide 2 foot contour layer.

    Data sources used in this process:
    • Ten 20-ft contour layers

    Data sources produced in this process:
    • Connecticut 2 Foot Contours (Revised)

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How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    Connecticut 2 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 2, 10, and 20 foot intervals. Attributes for LABEL_2, LABEL_10, and LABEL_20 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.

  2. How accurate are the geographic locations?

    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.

  3. How accurate are the heights or depths?

    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.

  4. Where are the gaps in the data? What is missing?

    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.

  5. How consistent are the relationships among the observations, including topology?

    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.

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How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access constraints: None. No restrictions or legal prerequisites for accessing the data. The data is in the public domain and may be redistributed.
Use constraints:
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.

Distributor 1 of 1

  1. Who distributes the data set?

    State of Connecticut, Department of Environmental Protection
    79 Elm Street
    Hartford, CT 06106-5127
    USA

    860-424-3540 (voice)
    860-424-4058 (FAX)
    dep.gisdata@ct.gov
    Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

  2. What's the catalog number I need to order this data set?

    Connecticut 2 ft Contours (Revised)

  3. What legal disclaimers am I supposed to read?

    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.

  4. How can I download or order the data?

    • Availability in digital form:


    • Data format:
      in format File Geodatabase (version ArcGIS 10)
      Network links:http://www.ct.gov/deep

    • Cost to order the data: A copy of the data may be accessed without charge


  5. Is there some other way to get the data?

    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.

  6. What hardware or software do I need in order to use the data set?

    Geographic information sytem (GIS), computer-aided drawing or other mapping software is necessary to display, view and access the information.

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Who wrote the metadata?

Dates:
Last modified: 20111207

Metadata author:
Courtney Larson
State of Connecticut, Department of Environmental Protection
79 Elm Street
Hartford, CT 06106-5127
USA

860-424-3540 (voice)
860-424-4058 (FAX)
dep.gisdata@ct.gov
Hours of Service: Monday to Friday, 08:30 to 16:30 Eastern Standard Time

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata(FGDC-STD-001-1998)

Metadata extensions used:
  • http://www.esri.com/metadata/esriprof80.html
  • http://www.esri.com/metadata/esriprof80.html

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