This is a special 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. However, the boundaries of the polygon features in this layer DO NOT correspond exactly with the quadrangle boundaries published on the USGS 7.5-minute 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 based on the Connecticut State Plane Coordinate System, North American Datum of 1927 (NAD27). However, the boundaries of the polygon features in this layer DO line up with the NAD83 reference tics shown at the corners of each quadrangle map. This index was generated by mathematically projecting the 7.5-minute latitude and longitude quadrangle corner coordinates to Connecticut State Plane Coordinate System, NAD83. It represents a true NAD83 index of 7.5-minute quadrangle areas. Each polygon feature defines a geographic area that is slightly different than the 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 7.5-minute quadrangle areas based on the Connecticut State Plane Coordinate System, North American Datum of 1983 (NAD83) rather than the Connecticut State Plane Coordinate System, North American Datum of 1927 (NAD27). All currently available quadrangle maps for Connecticut are based on (published in) NAD27. This layer is an index to a possible new series of 7.5 minute topographic quadrangle maps published by the USGS based on NAD83. Due to the change in horizontal datums, NAD83-based topographic quadrangle maps will cover slightly different geographic areas than the currently available set of USGS topographic quadrangle maps. The geographic area encompassed by USGS 7.5-minute quadrangle maps is based on a grid interval of 7.5 minutes of latitude and longitude. The quadrangle boundaries shown on the USGS 7.5 minute topographic quadrangle maps are generated by projecting the 7.5-minute latitude and longitude coordinates that define the corners of the 7.5 minute quadrangle maps to the Connecticut State Plane Coordinate System, NAD27, whereas the quadrangle index polygon boundaries for this layer are generated by projecting these same latitude and longitude coordinate values to the Connecticut State Plane Coordinate System, NAD83. Consequently, this layer represents a true NAD83 quadrangle index, but these quadrangle polygon boundaries are not exactly identical to and do not precisely lineup with the quadrangle boundaries printed on the current set of 1:24,000-scale USGS topographic quadrangle maps. For example, quadrangle index polygon boundaries running North-South (lines of longitude) are offset from the corresponding boundaries on the topographic quadrangle maps by about 125 feet, and the quadrangle index polygon boundaries running East-West (lines of latitude) are offset from the corresponding boundaries on the topographic quadrangle maps by about 35 feet. This discrepancy is expected because this layer's quadrangle index polygon features and the USGS topographic quadrangle maps are originally based two different horizontal datums (NAD83 and NAD27), resulting in the placement of latitude and longitude coordinate values at slightly different locations on the surface of the Earth. Use a different quadrangle index layer named USGS 7.5 Minute Quadrangle Index for quadrangle boundaries that correspond exactly with the boundaries of the USGS 7.5-minute topographic quadrangle maps.

In 2004, the State of Connecticut Department of Environmental Protection developed automated procedure to systematically create the USGS 7.5 Minute Quadrangle Index layer in order to officially document the process by which this layer was previously developed by this agency. This automated procedure was developed using ArcInfo Workstation 8.3 software and the Arc Macro Language (AML) as a scripting environment and recorded in an AML file named MAKEINDEX.AML for the USGS quadrangle map category of data for the State of Connecticut, Department of Environmental Protection. The MAKEINDEX.AML derives polygon features and assigns attribute information to these features based on information in three text files that specify and define polygon corner coordinates, polygon label point coordinates, and polygon attribute values.

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

None. The data is in the public domain and may be redistributed.

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 (NAD83 Area) layer, published by the CT DEP. Source map scale is 1:24,000.

Use the QUAD_NO attribute to uniquely identify features.

USGS 7.5 Minute Topographic Quadrangle areas represented as polygon features.

State of Connecticut, Department of Environmental Protection

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 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 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 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.

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.

Connecticut USGS 7.5 Minute Quadrangle Index (NAD83 Area)

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

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.