This is a mosaic of the U.S. Geological Survey digital raster graphics (DRG's) 7.5 minute topographic quadrangle maps that cover the State of Connecticut.  The source map scale of the map is 1:24,000-scale (1 inch = 2,000 feet). The elevation contour interval is 10 feet. This mosaic is based on seamless DRGs, which only include the main body of the topographic map without the map collar. Seamless DRGs do not have map collars and can be tiled together to create a seamless mosaic view of an area. 

A digital raster graphic (DRG) is a USGS data product. A DRG is a scanned image of a USGS standard series topographic map, including all map collar information. The image inside the map neatline is georeferenced to the surface of the earth and fit to the Universal Transverse Mercator projection. The horizontal positional accuracy and datum of the DRG matches the accuracy and datum of the source map. These topographic quadrangle maps were scanned by the USGS at a resolution of 250 dots per inch. The Connecticut Department of Environmental Protection projected DRGs produced by the USGS to the Connecticut Coordinate System, North American Datum of 1983 (NAD83). Map units are in feet.
				
Topographic maps show the location and shape of hills, valleys, rivers, streams, lakes, ponds, wooded areas, roads, railroads, trails, buildings, urban areas, political boundaries, and many other features. The colors on a topographic map are symbolic of different map features. Water is blue. Wooded areas are green. Contour lines are brown. Cultural feature such as buildings, place names, boundary lines, are black. Principal roads are red. Urban areas are pink. Photorevisions (updates) to older maps compiled from aerial photos are purple. For example, a new building is shown in solid purple, a new road is shown as a purple line, and a new pond is shown with diagonal line shading in purple. If an area has become urbanized, this may be shown as purple shading on the new, revised map.

Topographic contours are shown in brown by lines of different widths. Each contour is a line of equal elevation; therefore, contours never cross. They show the general shape of the terrain. To help determine elevations, index contours are shown as wider brown contour lines on the map. Elevation values are printed in several places along these index contours. The narrower intermediate and supplementary contours found between the index contours help to show more details of the land surface shape. Contours that are very close together represent steep slopes. Widely spaced contours or an absence of contours means that the ground slope is relatively level. The elevation difference between adjacent contour lines, called the contour interval, is selected to best show the general shape of the terrain.

1. Gentle slopes (low angle from horizontal) on topographic maps with a given interval will be represented by widely spaced contour lines.

2. Steep slopes (high angles from the horizontal) on topographic maps with a given contour interval will be represented by closely spaced contour lines. Thus, a vertical cliff large enough to be represented as a topographic feature would be represented by contour lines that merge (i.e., stacked together because of the 90 degree slope).

3. Contour lines that cross streams flowing through valleys of noticeable relief will form a V-shaped deflection with the apex of the V pointing upstream. This relationship between contour lines and stream valleys is referred to as the RULE of V's. Because a V will always point upstream, the orientation of V's can always be used to determine the direction of the slope of the surface as well as the direction of the flow of the water.

4. Concentric circles of contour lines indicate a hilltop; concentric circles with hachure marks indicate a closed depression.

The DRG is used for validating digital line graphs (DLG's) and for DLG data collection and revision. The DRG can help assess the completeness of digital data from other mapping agencies. It can also be used to produce hybrid data products. These include combined DRG's and digitial ortho quadrangles (DOQ) for revising and collecting digital data, DRG's and digital elevation models (DEM) for creating shaded-relief DRG's, and combinations of DRG, DOQ, and DLG data. Although a standard DRG is an effective mapping tool, its full potential for digital production is realized in combination with other digital data.

In 1997, the Connecticut Department of Environmental Protection published 3 sets of Connecticut DRG data products derived from DRGs produced by the USGS. All 3 data products are in the Connecticut State Plane Coordinate System North American Datum of 1983 (map units are feet). 
		
		1. Collared DRGs - Identical to U.S. Geological Survey DRG. Includes the main body of the topographic map with all map collar information such as the map border, legend, and marginalia information with quadrangle name, publication date, scale bar, grid coordinates, magnetic declination, etc. These Collared DRG tiles are in Tagged Image File Format (TIFF) format and named drgxxxx.tif, where xxxx is a 4 digit quadrangle number beginning at 0001.
		
		2. Seamless DRGs in TIFF format - Includes the main body of the topographic map without the map collar. Seamless DRGs do not have map collars and can be tiled together to create a seamless mosaic view of an area. These Seamless DRG tiles are in Tagged Image File Format (TIFF) format and named drg_quadxxxx.tif, where xxxx is a 4 digit quadrangle number beginning at 0001. Prior to 2007, these Seamless DRG tiles were named qxxxx.tif.
		
		3. Seamless DRGs in MrSID format - Includes the main body of the topographic map without the map collar. Seamless DRGs do not have map collars and can be tiled together to create a seamless mosaic view of an area. These Seamless DRG tiles are in a compressed image format, MrSID (Multiresolution Seamless Image Database; *.SID) by LizardTech, and named drg_quadxxxx.sid, where xxxx is a 4 digit quadrangle number beginning at 0001. The MrSID file compression results in a reduced image size and slight modification in color. Prior to 2007, these Seamless DRG tiles were named qxxxx.sid.

		In 1997, the Connecticut Department of Environmental Protection produced these DRG data products using USGS DRGs available at the time. Map publication dates varied from 1954 to 1992 and source map scale also varied slightly due to the availability of metric topographic maps. More recently published topographic quadrangle maps may be available from the USGS for some quadrangle areas. In all, the set of Connecticut DRGs were based on a combination of 7.5 minute map series (published at 1:24,000 scale) and 7.5 by 15 minute metric map series (published at 1:25,000 scale). Most Connecticut DRGs are based on 7.5 minute (1:24,000-scale) topographic maps. However, ten 7.5 minute topographic areas along the Connecticut-Massachusetts state boundary are published on 7.5 by 15 minute (1:25,000-scale) metric topographic maps, which include two 7.5 minute quadrangles per map sheet. The 7.5 by 15 minute metric topograpic maps were more current than previously published standard 7.5 minute quadrangles for these same areas. Consequently, seamless DRGs for the 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), Wales MA-CT (11), Southbridge MA-CT (12), Webster MA-CT (13), and Oxford MA-CT-RI (14) 7.5 minute quadrangles were cropped - along 7.5 minutes of latitude and 7.5 minutes of longitude - from the following USGS 7.5 by 15 minute metric (1:25,000 scale) quadrangle maps: Ashley Falls MA-CT-NY (1-2), Tolland Center MA-CT (3-4), Southwick MA-CT (5-6), Southbridge MA-CT (11-12), and Webster MA-CT-RI (13-14).

		For additional specific information on the production of digital raster graphics, refer to Standards for Digital Raster Graphics (National Mapping Program Technical Instructions) published by the U.S. Department of Interior, U.S. Geological Survey.

publication date

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

None. No restrictions or legal prerequisites for using the data after access is granted. 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 CT DEP and the USGS as the source for this information. For example, include the following data source description when printing this information on a map: Topo Map Information - From USGS Digital Raster Graphics. Source map scale is 1:24,000.

Each raster entity or pixel contains a digital index number from 0 through 12 referencing a color palette of red, green and blue (RGB) values from 0 through 255 in which the standard colors used in the DRG are defined. The index is a unique number. The color for each index value is stored as three numbers describing the amount of red, green, and blue light required to produce the color. 

The following documents the (red,green,blue) color values for index numbers 0 - 12 for a USGS DRG. 
			
		0 = (0,0,0) - Black 
		1 = (255,255,255) - White 
		2 = (0,151,164) - Blue 
		3 = (203,0,23) - Red 
		4 = (131,66,37) - Brown 
		5 = (201,234,157) - Green 
		6 = (137,51,128) - Purple 
		7 = (255,234,0) - Yellow 
		8 = (167,226,226) - Light Blue 
		9 = (255,184,184) - Light Red 
		10 = (218,179,214) - Light Purple 
		11 = (209,209,209) - Light Gray 
		12 = (207,164,142) - Light Brown

Note, Seamless DRGs partially overlap along their edges, resulting in the appearance of white borders between individual image tiles. To make all seamless DRG tiles appear truely seamless, cartographically removed their overlapping white edges from display using techniques to render white pixels (index number 1) with transparent symobology.

The USGS DRG is produced with the intention of replicating as close as possible the original source map.  Users of the DRG will note, however, that a certain amount of "noise" can be discerned when small areas are blown up or viewed under zoomed-in conditions. This noise is in the form of random specks or pixels of color and halos due to any number of factors, such as, the quality of the source, the use of screens and patterns on the litho, and the  unevenness of ink due to saturation and absorption.   Discontinuities or breaks in linear features may also be present and are due to improper calibration or usage of the scanner, the condition of the source, and  resampling.  Descreening, quantizing, and noise filtering are methods used to reduce noise, which, besides creating a more aesthetically pleasing image, have the added benefit of reducing the size of the image file.  Removal of lithographic screen patterns is preferred but not required.

Image completeness is checked by visually inspecting a sampling of DRG's.  Each selected DRG will be examined for gaps (missing data) in the main body of the map, the map collar, the overedge areas, and any insets.

The DRG uses a standard palette to ensure uniform color throughout a particular map series. The RGB values for a particular color, therefore, will remain consistent throughout that DRG series. Although the color values of the DRG may sometimes match those of the paper source map, a user will usually notice small differences between the colors on the digital image and on the paper map. Also, the quality of the user's monitor affects the DRG color displayed. Although the DRG generally contains the complete content of the source map, features may occasionally be blurred because of substandard source materials. The DRG also may contain misclassified pixels (color noise).
		
		The DRG is an 8-bit color image that employs a color palette to ensure uniform colors throughout a particular DRG series. All DRG's within a series must have the same RGB value.

The horizontal positional accuracy of this data meets the United States National Map Accuracy Standards (NMAS) for 1:24,000-scale maps. DRG's will retain the horizontal accuracy of the source maps. Most USGS printed maps contain the NMAS note in the collar area. The NMAS states that for maps on publication scales of 1:20,000 or smaller, not more than 10 percent of the points tested shall be in error by more than 1/50 inch measured on the publication scale.  Test points must be "well-defined", that is, easily visible or recoverable on the ground.  For DRG's this accuracy statement applies only to that area of the DRG that falls within the neatline of the source map (excluding inset areas).  Overedge areas falling outside the transformation boundary area (the map neatline), can exhibit anomalies or discrepancies. These anomalies also will appear in the map inset areas and in the map collar.  For maps without the NMAS note, the horizontal accuracy is unknown.  However, the DRG will retain the accuracy of the source map.

The vertical positional accuracy is referenced in the DRG map collar.

Statewide Mosaic of USGS 7.5 Minute Topographic Quadrangle Maps for Connecticut

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.

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.

None. No restrictions or legal prerequisites for accessing the metadata.

None. No restrictions or legal prerequisites for using the metadata after access is granted.