Digital Mapping Techniques '02 -- Workshop Proceedings
U.S. Geological Survey Open-File Report 02-370
Cartographic Observations from Production of the Surficial Geologic Map of Northern New Jersey
By James R. Estabrook, D. Paul Mathieux, and Will R. Stettner
U.S. Geological Survey
Eastern Publications Group
National Center, MS 903
12201 Sunrise Valley Drive
Reston, VA 20192
Telephone: (703) 648-4319
Fax: (703) 648-6138
e-mail: jestabro@usgs.gov
INTRODUCTION
The Surficial geologic map of northern New Jersey (Stone and others, 2002) is a cooperative endeavor between the New Jersey Geological Survey and the U.S. Geological Survey (USGS). It is the final in a series of four map products that show the bedrock and surficial geology of New Jersey at a scale of 1:100,000. New Jersey is the first state to have such coverage over its entire area. Field work for the northern surficial map was begun in 1982, and compilation was done between 1989 and 1995. This product consists of three large map sheets (40 x 56 inches) and a text pamphlet. Sheet 1 shows the map at a scale of 1:100,000, along with a correlation of map units and a list of map units; sheet 2 contains 11 supporting maps and figures; and sheet 3 displays 11 cross sections. The 41-page pamphlet contains a detailed description of map and subsurface units and presents stratotype sections for eight proposed lithostratigraphic units of Quaternary age in northern New Jersey. This map adjoins the Surficial geologic map of central and southern New Jersey (Newell and others, 2000). The cartographic production of that map was discussed in the Digital Mapping Techniques '01 Workshop Proceedings (Stettner and Koozmin, 2001). Many of the steps described therein were also applied to the production of this map.
Our purpose in writing this paper and presenting the map as a poster at DMT '02 is to discuss (1) how we assembled the base map, (2) author compilation, and (3) how we applied Adobe Illustrator software to cartographic production.
BASE MAP
The base map on which the geology is shown is from the USGS 1:100,000-scale series and consists of a mosaic of one entire quadrangle with parts of five adjoining quadrangles. Because the mosaic was constructed in the late 1980's, mosaicking was accomplished not by digital means but entirely by hand on a large light table; film positives of each quadrangle were trimmed of their marginal information, edge-joined to create a "seamless" base image, and carefully taped onto a clear-film carrier sheet. Actually, three mosaics were constructed in order to permit the printing of the base in three colors: blue for drainage, brown for topography, and gray for culture (roads and place names). To accomplish this, we obtained film positive "separates" of the drainage, topography, and culture for all six quadrangles ÐÐ 18 positives in all. The culture separates were mosaicked first; then, in turn, the drainage and topography separates were mosaicked, each on their own carrier sheet registered on top of the culture to ensure exact fit. Film positives were made from each mosaic, as well as a composite negative of all three mosaics; this negative was used to produce a greenline on which the authors began to compile their geology.
At the start of cartographic production, the film positives of the three mosaics were scanned at a resolution of 300 dpi as transparent line art for graphic processing in Adobe Illustrator. Because raster images by nature have a diminished legibility, we selected for the printing of the culture a solid gray ink, rather than black ink screened 50 percent biangle, to avoid further eroding the raster image. The 50-percent biangle screen normally is used in printing to reduce the intensity of base-map information by breaking up the image. It also diminishes the clarity of the image and therefore is not recommended for use in conjunction with a raster image. Using a solid gray ink achieves a subdued image without causing any loss of clarity. For drainage, we chose Pantone 300 blue rather than the conventional cyan. Pantone 300 blue is considerably darker than cyan, so the drainage remains legible where overprinted by geologic map units composed of high percentages of cyan.
At the completion of cartographic production, we generated printing negatives and made a cromalin proof to check the registration and colors and to see how well the base image stood up against the other map features. The USGS 1:100,000-scale quadrangle maps use Souvenir (serif) and Univers (sans serif) type fonts in various sizes. We observed on the proof that most sans-serif place names, even at a small size, were pretty legible, but that serif type, even in large place names, was difficult to read. The presence of dense road networks under many feature names contributed to the problem. We rescanned the culture mosaic at several higher thresholds of optical sensitivity, but at the same resolution (300 dpi), and eventually found a threshold that yielded clearer type and linework. The improved legibility of the serif type, especially in congested urban areas, was achieved by sacrificing the legibility of very fine lines, most noticeable in some secondary roads and route numbers in rural areas. Rescanning the culture required us to carefully monitor its registration with the drainage and topography.
AUTHOR COMPILATION
Showing features that resulted from glaciation of most of the map area added much to the intricacy of the map. The complexity of the map is reflected by the number of registered overlays the authors required in order to compile their data. In addition to the greenline showing contacts and map-unit labels, seven overlays were drafted, which contained the following data: (1) patterned-area outlines (seven categories); (2) outlines of areas of thin till cover; (3) artificial fill (solid color areas and patterned areas); (4) contours showing elevation of the bedrock surface relative to sea level; (5) drainage basin divides; (6) symbols; and (7) bedrock outcrops.
To construct a mill copy for editing, we made a greenline of the base map and photographically exposed the contacts and the other information from the seven overlays to this greenline, to show in black, red, or blue. The authors then used colored pencils to shade in the map units, with the intent of actually using the same color scheme they desired to see on the final printed map. The colored mill was useful as a general color guide; however, as there are more than 175 map units, we needed some vehicle to help us readily distinguish them on the mill copy because (1) colors had to be repeated for many units, and (2) the small size of most polygons prohibited the authors from labeling more than half of them. Adobe Illustrator software proved to be most helpful with the identification problem; it is discussed in the following section.
CARTOGRAPHIC PRODUCTION USING ADOBE ILLUSTRATOR
Until recently, when geologic maps (especially simpler ones) were undergoing review, our practice was to edit the author's mill copy, ask him to make any agreed-upon changes to the drafting on his greenline, and then import his linework into Adobe Illustrator to begin cartographic production. In an effort to streamline production, we are now importing all data sets (raster and vector) into Adobe Illustrator, separating data into individual layers, and making refinements and a preliminary layout, all prior to the technical edit. The edit and subsequent reviews are made on color plots run on a large-format Hewlett Packard 3000 DesignJet. Because of the ability in Adobe Illustrator to group geologic-feature layers in different combinations, we were able to make plots showing selected geology (specific layers) for a particular review and (or) edit. This gave us a flexibility we found to be indispensable. As a result of this option, we made and reviewed approximately 30 generations of plots during the course of producing the three map sheets.
Unidentified Polygons
The contacts, patterned-area outlines, thin-till-area outlines, and artificial fill were scribed in order to get scannable linework of uniform quality. We had a positive made from each scribecoat, then contracted with Geologic Data Systems, Inc. (GDS), of Denver, Colorado, to furnish a data set of each positive by scanning the positives and tagging the polygons represented on them. These data sets were created in AutoCAD. Once imported into Adobe Illustrator, they required extensive sorting and organizing. Initially, about 5,000 polygons (one-quarter of the map's total) could not be identified by GDS owing to complexity of the mill copy. Ultimately, a review plot was sent to the authors showing all unidentified polygons in red. Using the mill copy, related compilations, and their notes, the authors resolved the unidentified polygons.
Color Selection
Of the 175 map units, 40 represent meltwater sediments deposited in major glacial lakes, and 46 represent meltwater sediments deposited in small glacial lakes and ponds. For these two categories, limited segments of the spectrum ÐÐ blue to bluish green to gray for the former, and tan to violet to purple for the latter ÐÐ had to represent all 40 and 46 units, respectively. To map and correlate the meltwater deposits, the authors divided the map area into five geographic regions on the basis of physiography and watershed. Within each region, for each category of meltwater sediment, the youngest deposits were given the lightest color shades, and the oldest deposits the darkest shades. For both kinds of meltwater sediment, a few regions had as many as 14 units, so some repeating of colors was necessary. Within each meltwater-sediment category it was permissible to repeat colors from one region to another. The issue was to make sure no two adjoining units on the map had the same color. By having each map unit in its own layer, we were able to selectively view a unit on screen in combination with any other units whose color and proximity we wanted to verify. Adobe Illustrator provided a very efficient method for identifying color problems. In order to perform these operations, hardware with the maximum processing speed and RAM was essential. All digital manipulations were performed on an Apple Macintosh G4 computer having 500 MHz processing speed and 1.25-gigabyte RAM.
REFERENCES
Newell, W.L., Powars, D.S., Owens, J.P., Stanford, S.D., and Stone, B.D., 2000, Surficial geologic map of central and southern New Jersey: U.S. Geological Survey Miscellaneous Investigations Series Map I-2540-D, scale 1:100,000, 3 sheets and pamphlet.
Stettner, W.R., and Koozmin, E.D., 2001, Cartographic choices for the surficial geologic map of central and southern New Jersey, in Soller, D.R., ed., Digital Mapping Techniques '01 ÐÐ Workshop Proceedings: U.S. Geological Survey Open-File Report 01-223, p. 233-239.
Stone, B.D., Stanford, S.D., and Witte, R.W., 2002, Surficial geologic map of northern New Jersey: U.S. Geological Survey Miscellaneous Investigations Series Map I-2540-C, scale 1:100,000, 3 sheets and pamphlet.
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