This is an index of the 1:24,000-scale U.S. Geological Survey (USGS) 7.5-minute topographic quadrangle maps that cover the State of Connecticut. The index includes a polygon feature for each 7.5-minute quadrangle area. All polygon feature boundaries correspond exactly with the quadrangle boundaries depicted on the 7.5-minute topographic quadrangle maps published by the USGS because both are based on the Connecticut State Plane Coordinate System, North American Datum of 1927 (NAD27). Each polygon feature defines the same geographic area shown on the corresponding 1:24,000-scale USGS 7.5-minute topographic quadrangle map. Note, polygon attribute information is comprised of codes to uniquely identify individual quadrangle areas. This is static information that is not subject to change.
Use this layer to define the geographic area encompassed by the currently available set of 7.5-minute quadrangle maps published by the USGS, which are based on the Connecticut State Plane Coordinate System, North American Datum of 1927 (NAD27). For example, this layer can be used to clip or spatially query for map features in other layers that are located on a particular USGS 7.5-minute topographic quadrangle map. 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 7.5 minute quadrangle maps to the Connecticut State Plane Coordinate System, NAD27. Subsequently, these NAD27-based polygon areas were converted to the Connecticut State Plane Coordinate System, North American Datum of 1983 (NAD83) for consistency with other spatial data in NAD83. This geographic conversion or transformation process is commonly referred to as the North American Datum Conversion (NADCON) from NAD27 to NAD83. NADCON is the Federal standard for NAD27 to NAD83 datum transformations and is a tool for transforming coordinate values between datums. It does not improve the accuracy of the data. Also, it is important to note that as of the year this metadata was written (2005), all quadrangle maps for Connecticut were based on (published in) Connecticut State Plane Coordinate System, NAD27. None have been republished by the USGS in Connecticut State Plane Coordinate System, NAD83. For a true NAD83-based index, refer to a layer named USGS 7.5 Minute Quadrangle Index (NAD83 Area), which was generated by mathematically projecting the 7.5-minute latitude and longitude quadrangle corner coordinates directly to the Connecticut State Plane Coordinate System, NAD83.
CT DEP Quadrangle Numbers - The Connecticut Department of Environmental Protection established the following quadrangle numbers to uniquely identify 7.5 minute topographic quadrangle areas - Bashbish Falls MA-CT-NY (1), Ashley Falls MA-CT (2), South Sandisfield MA-CT (3), Tolland Center MA-CT (4), West Granville MA-CT (5), Southwick MA-CT (6), West Springfield MA-CT (7), Springfield South MA-CT (8), Hampden MA-CT (9), Monson MA-CT (10), Wales MA-CT (11), Southbridge MA-CT (12), Webster MA-CT (13), Oxford MA-CT-RI (14), Millerton NY-CT (15), Sharon CT-NY (16), South Canaan CT (17), Norfolk CT (18), Winsted CT (19), New Hartford CT (20), Tariffville CT-MA (21), Windsor Locks CT (22), Broad Brook CT (23), Ellington CT (24), Stafford Springs CT (25), Westford CT (26), Eastford CT (27), Putnam CT (28), Thompson CT-RI (29), Amenia NY-CT (30), Ellsworth CT (31), Cornwall CT (32), West Torrington CT (33), Torrington CT (34), Collinsville CT (35), Avon CT (36), Hartford North CT (37), Manchester CT (38), Rockville CT (39), Coventry CT (40), Spring Hill CT (41), Hampton CT (42), Danielson CT (43), East Killingly CT-RI (44), Dover Plains NY-CT (45), Kent CT (46), New Preston CT (47), Litchfield CT (48), Thomaston CT (49), Bristol CT (50), New Britain CT (51), Hartford South CT (52), Glastonbury CT (53), Marlborough CT (54), Columbia CT (55), Willimantic CT (56), Scotland CT (57), Plainfield CT (58), Oneco CT-RI (59), Pawling NY-CT (60), New Milford CT (61), Roxbury CT (62), Woodbury CT (63), Waterbury CT (64), Southington CT (65), Meriden CT (66), Middletown CT (67), Middle Haddam CT (68), Moodus CT (69), Colchester CT (70), Fitchville CT (71), Norwich CT (72), Jewett City CT (73), Voluntown CT-RI (74), Brewster NY-CT (75), Danbury CT (76), Newtown CT (77), Southbury CT (78), Naugatuck CT (79), Mount Carmel CT (80), Wallingford CT (81), Durham CT (82), Haddam CT (83), Deep River CT (84), Hamburg CT (85), Montville CT (86), Uncasville CT (87), Old Mystic CT (88), Ashaway RI-CT (89), Peach Lake NY-CT (90), Bethel CT (91), Botsford CT (92), Long Hill CT (93), Ansonia CT (94), New Haven CT (95), Branford CT (96), Guilford CT (97), Clinton CT (98), Essex CT (99), Old Lyme CT (100), Niantic CT (101), New London CT-NY (102), Mystic CT-NY-RI (103), Watch Hill RI-CT (104), Mount Kisco NY-CT (105), Pound Ridge NY-CT (106), Norwalk North CT-NY (107), Westport CT (108), Bridgeport CT (109), Milford CT (110), Woodmont CT (111), Glenville CT-NY (112), Stamford CT (113), Norwalk South CT (114), Sherwood Point CT-NY (115), Mamaroneck NY-CT (116), Unpublished Quad (1213), Unpublished Quad (1214), Unpublished Quad (1215), Unpublished Quad (1216), Orient NY (1217), Plum Island NY (1218), Unpublished Quad (1310), Unpublished Quad (1311), Unpublished Quad (1312), Unpublished Quad (1313), Bayville NY (1407), and Lloyd Harbor NY (1408). The USGS does not publish 7.5 minute topographic quadrangle maps for quad numbers 1213, 1214, 1215, 1216, 1310, 1311, 1312, and 1313. These quadrangles are either located in the middle of Long Island Sound (and are entirely coved by water) or include small land areas along the coast shown on the southern margins of the Branford CT (96), Guilford CT (97), Clinton CT (98) topographic quadrangle maps. The Branford, Guilford, and Clinton topographic maps include areas along the Connecticut shoreline slightly beyond their southern quadrangle boundary, which is defined as 41 degrees and 15 minutes of latitude. The additionally mapped areas on these 3 quadrangle maps include locations such as the Thimble Islands, Sachems Head, and Hammonnasset Point. These areas are actually located on unpublished quadrangles located to the south of the Branford, Guilford, and Clinton quadrangles - numbers 1213, 1214, and 1215. Unpublished quadrangle 1214 also covers Faulkners Island, which is in Long Island Sound off Guilford, Connecticut. The Orient NY (1217), Plum Island NY (1218), Bayville NY (1407), and Lloyd Harbor NY (1408) quadrangles include portions of Connecticut waters along the Connecticut-New York state boundary in Long Island Sound in addition to sections of Long Island, New York. These quadrangle maps do not contain any Connecticut landmass.
publication date
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 as the source for this information. For example, include the following data source description when printing this layer on a map: Quadrangle Boundary - From the USGS 7.5 Minute Quadrangle Index layer, published by the CT DEP. Source map scale is 1:24,000.
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The USGS 7.5 Minute Topographic Quadrangle Index layer depicts the quadrangle boundary feature type shown on the 7.5 minute USGS topographic quadrangle maps as polygon features with boundaries originally based on a NAD27 horizontal datum 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 QUAD_NO attribute values was conducted by manually entering and visually inspecting and verifying the 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 quadrangle index polygon features for all of Connecticut, 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.
Coordinates defining corners of 7.5 minute quadangle maps used to generate Tic registration features (Tic ID, Longitude, Latitude). Example values for one row of quadrangles: 806,-73.75000,41.75000 807,-73.62500,41.75000 808,-73.50000,41.75000 809,-73.37500,41.75000 810,-73.25000,41.75000 811,-73.12500,41.75000 812,-73.00000,41.75000 813,-72.87500,41.75000 814,-72.75000,41.75000 815,-72.62500,41.75000 816,-72.50000,41.75000 817,-72.37500,41.75000 818,-72.25000,41.75000 819,-72.12500,41.75000 820,-72.00000,41.75000 821,-71.87500,41.75000 822,-71.75000,41.75000 823,-71.62500,41.75000 906,-73.75000,41.62500 907,-73.62500,41.62500 908,-73.50000,41.62500 909,-73.37500,41.62500 910,-73.25000,41.62500 911,-73.12500,41.62500 912,-73.00000,41.62500 913,-72.87500,41.62500 914,-72.75000,41.62500 915,-72.62500,41.62500 916,-72.50000,41.62500 917,-72.37500,41.62500 918,-72.25000,41.62500 919,-72.12500,41.62500 920,-72.00000,41.62500 921,-71.87500,41.62500 922,-71.75000,41.62500 923,-71.62500,41.62500
Index is in ArcInfo coverage format with polygon and tic features.
Index 27 is in ArcInfo coverage format with polygon and tic features.
Quad_Index.shp is in ESRI Shapefile format with polygon features.
Quad Index is in GeoDatabase Feature Class format
Create Quadrangle Index - The quadrangle index polygon and tic registration features were mathematically created using ArcInfo 4 software to generate boundary line and tic registration features from latitude and longitude values that define the corners of the USGS 7.5 minute topographic quadrangle map that cover the State of Connecticut. For example, an initial ArcInfo coverage was generated to store (preliminary quadrangle boundary) line features based on a fishnet-type grid orientation with an origin of -73.45,40.875 (SW corner of quad 116), an upper left coordinate of -73.75,42.25 (NW corner of quad 406), an upper right coordinate of -71.625,42.25 (NE corner of quad 422), and a cell size of 0.125,0.125 (7.5 minutes). These features represented lines of latitude and longitude spaced at 7.5-minute intervals. Tic features were also generated and added to this coverage base on coordinate values from Source 1 (tics.txt). Spatial data was initially represented in Geographic Coordinates (unprojected units of latitude and longitude). In preparation for projecting the data to the Connecticut State Plane Coordinate System, five evenly spaced vertices were programmatically added along all quadrangle boundaries. This would allow line features to properly curve at vertex locations as opposed to simply projecting a straight line between quadrangle corners. The USGS 7.5 minute topographic quadrangle map are published in the Connecticut State Plane Coordinate System of 1927 (NAD27) so the quadrangle boundaries shown on these maps are not depicted as straight lines. Five vertices were programmatically added to each quadrangle boundary line feature at an interval of 0.021 minutes (0.125 / 6 = 0.021). Note, five vertices require 6 segments. ArcInfo coverage Fuzzy and Dangle tolerance settings were set to 4 and 0 (zero) feet, respectively. Based on the line feature geometry, polygon features were built and added to the Quadrangle Index Coverage, followed by manually attributing each polygon feature with the corresponding quadrangle number and quadrangle name information. Using ArcInfo 4 software, the coverage was projected from Geographic Coordinates to the Connecticut State Plane Coordinate System, North American Datum of 1927 (NAD27) to match the datum used by the USGS to publish the 1:24,000-scale 7.5 minute topographic quadrangle map series. The name of the resulting ArcInfo Coverage is INDEX.
Datum conversion - Using ESRI ArcInfo software, the Hydrography Master layer was converted from the Connecticut State Plane Coordinate System of 1927 (NAD27) to the Connecticut State Plane Coordinate System of 1983 (NAD83). The North American Datum Conversion (NADCON) data transformation was used.
Export to Shapefile Format - Converted polygon feature data from ArcInfo Coverage named INDEX27 to a Shapefile named Quad_Index.shp. Excluded the AREA, PERIMETER, INDEX27#, and INDEX27-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 Quad_Index; and imported the attribute definitions, loaded features and imported metadata from Quad_Index.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
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 Name - Name of the quadrangle map published by the USGS
US Geological Survey
Feature geometry.
ESRI
Use the QUAD_NO attribute to uniquely identify features.
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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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