Robert A. Renken, comp. 19981101 version 1.0 digital data Reston, Virginia U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?aquifers_pr This is polygon data of shallowest principal aquifers of Puerto Rico and the United States Virgin Islands, developed as part of the effort to produce a map published at 1:500,000 in Chapter HA 730-N of the "Ground Water Atlas of the United States" series of printed publications. See Other_Citation_Details for publication information. The published map contains base and cultural features not included in this data. The Ground Water Atlas publication also includes information that may be relevant to the use of this data, such as figures showing where an aquifer may extend beyond the area delineated in this data, but be overlain by one or more other aquifers and/or low-permeability material. The areal extent of the aquifers, as shown in this data, represent the area in which a named aquifer is the shallowest of the principal aquifers. These aquifer areas are not necessarily the only area in which ground water can be withdrawn because the aquifers shown may have a larger areal extent than is represented here. The boundaries in this data generally represent an interpretation of the surface location (outcrop), or near surface location (shallow subcrop) of the uppermost principal aquifer for the area. An aquifer may extend beyond the area shown in this data, but be overlain by one or more other aquifers, and/or low-permeability material. These aquifer outcrop and shallow subcrop boundaries represent broad, regional categories and should not be interpreted as site specific. Comments regarding the names of aquifers, or the hydrogeologic interpretation of the aquifers can be can be directed to the USGS Water Resources Division, Office of Ground Water, Roy Sonenshein, sunshine@usgs.gov, (305) 526-2895. For publications, at a scale of 1:500,000 or smaller. Because of the small scale, the primary use is for regional and national data display rather than specific local data analysis. Introduction This data was created as part of the effort to produce an aquifer map published at 1:500,000 in Chapter HA 730-N of the "Ground Water Atlas" series of printed publications. See reference for more publication details. Since this data was created to produce a printed map, the map can be considered the source for the data. The information below is provided for more detail regarding the map's compilation procedures. The coverages for Puerto Rico, and the Virgin Islands were processed separately, and later appended into one coverage. The processing steps are discussed separately for Puerto Rico, and the Virgin Islands PUERTO RICO *Aquifer contact lines The aquifer contact information was originally compiled by Robert A. Renken at a scale of 1:250,000 on scale-stable material. The contacts were scribed at a lineweight of 0.004". Several lat-long intersections were also scribed for later use in georeferencing. A film positive made from the scribecoat was scanned at a resolution of either 300 or 400 pixels per inch (exact resolution was not recorded). The raster image was converted to an Arc/Info grid and vectorized using the Arcscan module with these parameters: ArrowLength 32 ArrowWidth 3 BackTrack YES BRANCH STRAIGHT DASH 0.033 EndOfLine NOMANUAL EndOfSession EDIT FAN 15.000,30.000 ForeGround 1 GAP 0.025 GeneralizeTOLerance 0.005 HOLE 0.002 JunctionSensitivity MEDIUM LineSymbol 8 LineVariation 2.000 LineWidth 14.000 MarkerSymbol 0 MODE CENTER RegionOfInterest 9999.000,9999.000,-9999.000,-9999.000 RETRACE NO SearchRadius 10.000 SKIP 0 STraightenAngle 0.000 STraightenCorner 0.000 STraightenDistance 0.000 STraightenRange 0.000 The resulting lines were edited in Arcedit for completeness and vectorizing errors. Paper plots were made to compare the resulting linework to the original compilation. Discrepancies were noted and corrected. The low generalize tolerance used in the vectorizing process resulted in lines that closely matched the original compilation, but had a small vertex spacing. This small vertex spacing would have in turn resulted in large file sizes and an unnecessary level of detail for the intended publication scale. The arcs were generalized, splined, generalized, and unsplit in Arcedit, tolerances were not recorded. The appearance and accuracy of the resulting linework was judged against publication standards for the intended publication scale (1:500,000). The aquifer contact lines were transformed into their proper projection through the use of tic features located at several latitude- longitude intersections included in the scribed linework. The resulting RMS error was not recorded. The coverage was plotted and checked against the source compilation. Coastline The coastline was derived from an Arc/info coverage received from the USGS Water Resources Division Caribbean District in January, 1996. This coverage had been originally created from 1:20,000 USGS maps, and subsequently modified by the Caribbean Disctrict for use at a smaller scale. This coverage, as received contained more detail than was needed for the intended publication scale for the aquifer map (1:500,000). The coastline coverage was generalized for publication purposes, and the generalized version is now part of this data. The data linework was generalized by converting the line coverage into a grid , with a cell spacing of 25 meters. This grid was vectorized in Arcedit, using the Arcscan module. The parameters for vectorizing were: ArrowLength 32 ArrowWidth 3 BackTrack YES BRANCH STRAIGHT DASH 500.000 EndOfLine NOMANUAL EndOfSession EDIT FAN 45.000,90.000 ForeGround 1 GAP 0.025 GeneralizeTOLerance 25.000 HOLE 25.000 JunctionSensitivity MEDIUM LineSymbol 3 LineVariation 2.000 LineWidth 400.000 MarkerSymbol 0 MODE CENTER RegionOfInterest 9999.000,9999.000,-9999.000,-9999.000 RETRACE NO SearchRadius 375.000 SKIP 0 STraightenAngle 15.000 STraightenCorner 30.000 STraightenDistance 250.000 STraightenRange 750.000 This procedure resulted in a less detailed version of the original coastline. The resulting coastline was compared onscreen to the original. The aquifer contact lines were snapped to, and appended with the final coastline. Polygons were attributed in Arcedit. -------------------------------- VIRGIN ISLANDS *Aquifer contact lines The aquifer contact information was originally compiled by Robert A. Renken at a scale of 1:100,000 on scale-stable material. The contacts were scribed at a lineweight of 0.006". Several lat-long intersections were also scribed for later use in georeferencing. A film positive made from the scribecoat was scanned at a resolution of of either 300 or 400 pixels per inch (exact resolution was not recorded). The raster image was converted to an Arc/Info grid and vectorized using the Arcscan module with these parameters: ArrowLength 32 ArrowWidth 3 BackTrack YES BRANCH STRAIGHT DASH 0.033 EndOfLine NOMANUAL EndOfSession EDIT FAN 45.000,90.000 ForeGround 1 GAP 0.025 GeneralizeTOLerance 0.005 HOLE 0.002 JunctionSensitivity MEDIUM LineSymbol 8 LineVariation 2.000 LineWidth 5.000 MarkerSymbol 0 MODE CENTER RegionOfInterest 9999.000,9999.000,-9999.000,-9999.000 RETRACE YES SearchRadius 1.000 SKIP 0 STraightenAngle 0.000 STraightenCorner 30.000 STraightenDistance 0.000 STraightenRange 0.000 The resulting lines were edited in Arcedit for completeness and vectorizing errors. Paper plots were made to compare the resulting linework to the original compilation. Discrepancies were noted and corrected. The low generalize tolerance used in the vectorizing process resulted in lines that closely matched the original compilation, but had a small vertex spacing. This small vertex spacing that would have in turn resulted in large file sizes and an unnecessary level of detail for the intended publication scale. The arcs were generalized, splined, generalized, and unsplit in Arcedit, tolerances were not recorded. The appearance and accuracy of the resulting linework was judged against publication standards for the intended publication scale (1:500,000). The aquifer contact lines were transformed into their proper projection through the use of tic features located at several latitude- longitude intersections included in the scribed linework. The resulting RMS error was not recorded. The coverage was plotted and checked against the source compilation. Coastline The coastline was derived from coverages originally digitized from 1:24,000 USGS maps, as received from the USGS Water Resources Division Caribbean District in early 1992. These coverages contained more detail than was needed for the intended publication scale for the aquifer map (1:500,000). The coverages were appended, and edited to contain only coastline information. The coastline coverage was generalized for publication purposes, and the generalized version is now part of this data. The data linework was first generalized to a level of detail subjectively considered appropriate for display at a scale of 1:250,000. This was done by converting the line coverage into an Arc/Info grid, cell spacing unrecorded. This grid was vectorized in Arcedit, using the Arcscan module. The parameters for vectorizing were: ArrowLength 32 ArrowWidth 3 BackTrack YES BRANCH STRAIGHT DASH 1500.000 EndOfLine NOMANUAL EndOfSession EDIT FAN 45.000,90.000 ForeGround 1 GAP 25.000 GeneralizeTOLerance 0.500 HOLE 75.000 JunctionSensitivity MEDIUM LineSymbol 3 LineVariation 2.000 LineWidth 1200.000 MarkerSymbol 0 MODE CENTER RegionOfInterest 9999.000,9999.000,-9999.000,-9999.000 RETRACE YES SearchRadius 1125.000 SKIP 0 STraightenAngle 15.000 STraightenCorner 30.000 STraightenDistance 750.000 STraightenRange 2250.000 This procedure resulted in a less detailed version of the original coastline. This coastline was used in an intermediate compilation step, and was further generalized for publication at 1:500,000. The further generalization presumably included the use of the Arcedit generalize command, as well as on-screen editing, and use of cartographic judgement, however, records were not kept. The resulting coastline was compared onscreen to the original. The aquifer contact lines were snapped to, and appended with the final coastline. Polygons were attributed in Arcedit. The Puerto Rico, and Virgin Islands coverages were appended to create one coverage. The coverage was used to generate an output file that was imported by Adobe Illustrator for map publication. The completed map, at a scale of 1:500,000, was reviewed for content and accuracy by the Ground Water Atlas HA 730-N lead cartographer, Water Resources Division Geohydrologic Map Editor, and chapter author. Related Spatial and Tabular Data Sets_ A data set of principal aquifer outcrops of the 48 contiguous United States is available at: http://water.usgs.gov/lookup/getspatial?/aquifers_us A data set showing the extent of glacial deposits in the contiguous U.S. is in progress, as of 8/25/98. A data set of aquifers of Alaska will be available Nov 1 1998 at: http://water.usgs.gov/lookup/getspatial?/aquifers_ak A data set of aquifers of Hawaii is planned. 19981101 publication date Complete As needed -67.95023603 -64.55776822 18.5132586 17.67259591 None aquifer groundwater inlandWaters None Puerto Rico Virgin Islands United States Virgin Islands St. Croix St. John St. Thomas United States None Use at map scales of 1:500,000 or smaller Cidney J. Freitag U.S.Geological Survey mailing and physical address

505 Science Drive

Madison WI 53711-1061 USA 1-888-275-8747 This data was created and modified by Steven M. Bolssen and Cidney J. Freitag of the U.S. Geological Survey Water Resources Division Cartographic and Publications Program in Madison, Wisconsin between March 1996 and July 1997. Completion of this data and metadata was funded, in part, under a cooperative joint funding agreement between the U.S. Geological Survey and the U.S. Environmental Protection Agency. n/a Unclassified n/a Data General UNIX, ARC/INFO version 7.04 Accuracy of attributes tested by manual comparison of the source with hard copy plots and/or onscreen display and query of the data. Polygon and chain-node topology present. Each polygon is closed and has one label point. Complete Olcott, P.G. Renken, R.A., comp. 1997 1.0 map Hydrologic Investigations Atlas HA 730-N Reston, VA U.S. Geological Survey n/a 250000 stable-base material Unknown publication date GWA chapter HA 730-N Puerto Rico Olcott, P.G. Renken, R.A., comp. 1997 1.0 map Hydrologic Investigations Atlas HA 730-N Reston, VA U.S. Geological Survey n/a 100000 stable-base material Unknown publication date GWA chapter HA 730-N U.S. Virgin Islands See Supplemental_Information_Section regarding processing. n/a unknown n/a See Supplemental_Information_Section regarding processing. n/a unknown n/a Vector Point 486 String 1191 GT-polygon composed of chains 486 Albers Conical Equal Area 18.03333333333 18.43333333333 -65.6666666666 17.83333333333 0.0 0.0 coordinate pair 1.0 1.0 meters Puerto Rico Datum 1940 Clarke 1866 6378206.4 294.98 praqv1.PAT Polygon Attribute Table N/A AREA Area of polygon in square coverage units Computed Positive real numbers n/a n/a PERIMETER Perimeter of polygon in coverage units Computed Positive real numbers n/a n/a praqv1# Internal feature number Computed Sequential unique positive integer n/a n/a praqv1-ID User-assigned feature number user-assigned Integer n/a n/a rock_name Rock unit name Assigned See description in Entity_and_Attribute_Overview section n/a n/a rock_type Code number relating to rock unit name Assigned 100, 999 n/a n/a aq_name Aquifer unit name Assigned See description in Entity_and_Attribute_Overview section n/a n/a aq_code Code number relating to aquifer unit name Assigned See description in Entity_and_Attribute_Overview section n/a n/a praqv1.aat Arc attribute table n/a FNODE# Internal number of from-node Computed Sequential unique positive integer n/a n/a TNODE# Internal number of to-node Computed Sequential unique positive integer n/a n/a LPOLY# Internal number of polygon to left of arc Computed Sequential unique positive integer n/a n/a RPOLY# Internal number of polygon to right of arc Computed Sequential unique positive integer n/a n/a LENGTH Length of arc in coverage units Computed Positive real numbers n/a n/a praqv1# Internal feature number Computed Sequential unique positive integer n/a n/a praqv1-ID User-assigned feature number User-defined Integer n/a n/a LNTYPE Line category Assigned 1,2 lntype = 1 coastline lntype = 2 interior aquifer contact line n/a n/a Each principal aquifer is classified a type of permeable geologic material. There should be a direct correlation between the values of the rock_type and rock_name attributes, and between the aq_name and aq_code attributes. rock_type -- rock_name 0 -- null value, assigned to null polygon 100 -- unconsolidated sand and gravel aquifers 900 -- mentioned in Ground Water Atlas, but not a principal aquifer (field left blank) 999 -- Not a principal aquifer (field left blank) aq_code -- aq_name 0 -- null value, assigned to null polygon 114 -- Puerto Rico South Coast aquifer 115 -- Puerto Rico alluvial-valley aquifer 4191 -- North coast Limestone aquifer system upper aquifer 4192 -- North coast Limestone aquifer system lower aquifer 420 -- Kingshill aquifer 907 -- Coastal embayments aquifers 908 -- Volcaniclastic-, igneous-, and sedimentary-rock aquifers 997 -- Confining unit 999 -- Not a principal aquifer (field left blank) See publication references in Other_Citation_Details section U.S. Geological Survey Ask USGS - Water Webserver Team mailing

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://water.usgs.gov/user_feedback_form.html Although this data set has been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Export Coverage Win zipped 435 kb http://water.usgs.gov/GIS/dsdl/aquifers-pr.e00.zip Export Coverage zipped 1 http://water.usgs.gov/GIS/dsdl/aquifers-pr.e00.gz None. This dataset is provided by USGS as a public service. 20041108 U.S. Geological Survey Ask USGS -- Water Webserver Team mailing

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+aquifers_pr FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998