This is an index of the 3.75-minute quarter quadrangle areas that cover the State of Connecticut. There are four 3.75-minute quarter quadrangles per 7.5-minute quadrangle area. The index includes a polygon feature for each 3.75-minute quarter quadrangle area. Note that the boundaries of the polygon features in this layer DO NOT correspond exactly with the quadrangle boundaries published on the topographic quadrangle maps because the polygon feature boundaries are based on the Connecticut State Plane Coordinate System, North American Datum of 1983 (NAD83) and the boundaries on the quadrangle maps are base on the Connecticut State Plane Coordinate System, North American Datum of 1927 (NAD27). This index was generated by mathematically projecting the 3.75-minute latitude and longitude quarter quadrangle corner coordinates to Connecticut State Plane Coordinate System, NAD83. It represents a true NAD83 index of 3.75-minute quadrangle areas. Polygon attribute information is comprised of codes to uniquely identify individual quarter quadrangle areas. This is static information that is not subject to change.
Use this layer as an index to the set of USGS Digital Orthophoto Quarter Quadrangles published by the U.S Geological Survey, in cooperation with U.S. Department of Agriculture and the Connecticut Department of Environmental Protection. The USGS Digital Orthophoto Quarter Quadrangle (DOQQ) photos for Connecticut were published at 1:12,000 scale and are available from the State of Connecticut, Department of Environmental Protection.
publication date
No restrictions or legal prerequisites for using the data. 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 as the source for this information. For example, include the following data source description when printing this layer on a map: Quarter Quadrangle Boundary - From the USGS 3.75 Minute Quarter Quadrangle Index (NAD83 Area) layer, published by the CT DEP. Source map scale is 1:24,000.
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The USGS 3.75 Minute Quarter Quadrangle Index layer depicts the quarter quadrangle areas for the 7.5 minute USGS topographic quadrangle maps as polygon features with boundaries originally based on a NAD83 horizontal datum rather than NAD27 used by the USGS to publish the topographic quadrangle maps. All attributes have valid values. Values are within defined domains. The accuracy test for the QGNO, QUAD_NO, QUAD_SEC, and CTQUAD_FLG attribute values were conducted by manually entering and visually inspecting and verifying values. The QUADRANGLE attribute is the English language equivalent of (decodes) the QUAD_NO field values and was populated by joining the feature attribute data table to a lookup data table with QUAD_NO used as the relate key field. This lookup data table contain records with information that account for the unique occurrences of QUAD_NO.
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. 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 0 (zero) feet (dangle length).
The degree of completeness is based on the extent to which the data covers the geographic area of the State of Connecticut. The layer is complete because it includes four 3.75 minute quarter quadrangle polygon features for all of Connecticut 7.5 minute quadrangle areas, including areas defined by 7.5 minutes of latitude and longitude where the USGS published 1:24,000-scale topographic quadrangle maps and areas of 7.5 minutes of latitude and longitude entirely covered by water (in Long Island Sound) where the USGS did not publish 7.5 minute topographic quadrangle maps.
The horizontal positional accuracy of this data complies with the United States National Map Accuracy Standards for 1:24,000 scale maps. According to this standard, not more than 10 percent of the locations 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.
Indexqq is in ArcInfo coverage format with polygon and tic features.
Quarter_Quad_Index_NAD83_Area.shp is in ESRI Shapefile format with polygon features.
Quarter_Quad_Index_NAD83_Area is in GeoDatabase Feature Class format
The polygon boundaries for this layer were not manually digitized but rather mathematically generated by projecting the latitude and longitude coordinate values that define the corners of the 3.75-minute quarter quadrangle areas to the Connecticut State Plane Coordinate System, North American Datum of 1983 (NAD83). The latitude and longitude coordinates of the four corners for each quarter quadrangle formed the end points of four line features that bound each polygon feature. These lines of latitude and longitude spaced at 3.75-minute intervals were generated for the purpose of creating quarter quadrangle polygon features.
Export to Shapefile Format - Converted polygon feature data from ArcInfo Coverage named INDEXQQ to a Shapefile named Quarter_Quad_Index_NAD83_Area.shp. Excluded the AREA, PERIMETER, INDEXQQ#, and INDEXQQ-ID attributes from the Shapefile because their values are only maintained by ArcInfo software with data that is in ArcInfo Coverage format.
Convert to GeoDatabase Feature Class format - Defined new Feature Class named Quarter_Quad_Index_NAD83_Area; and imported the attribute definitions, loaded features and imported metadata from Quarter_Quad_Index_NAD83_Area.shp shapefile. Spatial Reference Properties for Feature Class: Coordinate System: NAD_1983_StatePlane_Connecticut_FIPS_0600_Feet XY Domain MinX: 100000; MaxX: 2247483.645 XY Domain MinY: 200000; MaxY: 2347483.645 Precision: 1000
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Internal feature number.
ESRI
Geographic Quadrangle Number - An ID number designated by the State of Connecticut, Department of Environmental Protection, Natural Resources Center in the 1980's to uniquely identify individual quadrangle maps that cover Connecticut and adjacent areas of Massachussets, New York and Rhode Island.
State of Connecticut, Department of Environmental Protection
Quadrangle Number - An ID number designated by the State of Connecticut, Department of Environmental Protection, Natural Resources Center in the 1980's to uniquely identify individual quadrangle maps.
State of Connecticut, Department of Environmental Protection
Quadrangle Section
State of Connecticut, Department of Environmental Protection
Northeast quarter quadrangle
Northwest quarter quadrangle
Southeast quarter quadrangle
Southwest quarter quadrangle
Quadrangle Name - Name of the quadrangle map published by the USGS
State of Connecticut, Department of Environmental Protection
Connecticut Quad Flag - Identifies quadrangles that cover the State of Connecticut
State of Connecticut, Department of Environmental Protection
True
False
Feature geometry.
ESRI
Use the QUAD_NO attribute to distinguish individual USGS topographic quadrangle areas. Use the QUAD_SEC attribute to distinguish between the four quadrants (NE, NW, SE, and SW) for each topograhic quadrangle area. Combine (concatinate) the QUAD_NO and QUAD_SEC attribute values to uniquely identify quarter quadrangle polygon features. For example, the four quarter quadrangle polygon features for the Clinton quadrangle (quadrangle number 98) are 98NE, 98NW, 98SE, and 98SW. Use the Connecticut Quadrangle Flag attribute (CTQUAD_FLG) to select quadrangles that cover the geographic area for the State of Connectictut with the following expression - CTQUAD_FLG = "T".
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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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