Textural patterns for geologic map making

Mark Neuhaus

June 4, 2002

A bit of history first.

We used to produce 28 by 40 inch, multi-color geologic maps, printed on an offset press. We would manually scribe the lines on scribecoat material, burn peelcoats from these scribes, and paste up clear lettering films. Due to the complexity of the maps, we would often need to use pattern overprints or knockouts in order to delineate the various geologic units. For this purpose, we would insert zip-a-tone, or equivalent, patterns in our open window negatives to produce these effects.

When we went to digital mapmaking with MicroStation, a fine CAD package, we needed to have a way to use similar patterns. MicroStation has a feature called cell libraries, in which one stores symbols that can be used to decorate a line or flood an area. We designed a handful of cells that effectively duplicated the common patterns we used, and applied them in various weights, colors, and scales to the geology polygons. Straight from MicroStation, we were able to make postscript files that were sent to an imagesetter to produce screened, composite, color separated negatives to be used on the offset press.

When it was decided that we were going to plot our maps instead of print them, we switched to MapInfo. We were very disappointed to see the limited pattern selection and the even poorer plotted quality of the patterns. I read with interest the techniques on Jacques Paris's page and thought there must be an easier way. Or at least, another way.

Our solution

I hoped that I might be able to bring my MicroStation patterns into MapInfo, so I thought I'd try an experiment. Since most of our mapping is USGS quadrangle based, I drew a rectangle in MicroStation that was larger than a typical quad in Oregon. MicroStation uses orthogonal coordinates, so I set it up in meters to be able to use UTM coordinates. I then filled the rectangle with various patterns and saved them in individual files. I used the universal translator in MapInfo to import them, and I now had vector lines of the patterns. Lines of varying spacing and angles, diamond lines, randomly placed open triangles or circles. Whatever I wanted to try. Now I have files of patterns that cover a whole quad, just like a giant piece of zip-a-tone.

Next, the patterning of the unit polygons. I pulled up a geology polygon map and selected all polygons of one unit type, such as landslide. I saved this selection to a new file with an appropriate unit name. I then opened only the new file and the selected pattern file, in this case, randomly placed triangles. Select the pattern file and make it the target. Then use the polygon file and erase outside. While the resultant pattern elements are still highlighted, I copy them to the clipboard. I revert and remove the pattern file from the mapper window, keeping it intact for future use. This leaves just the landslide unit polygon file there and I then do a paste, which inserts the triangle pattern elements that were left after erasing outside. Select all elements in this mapper and turn the polygon boundaries to null, and I now have a file with just the landslide pattern in the polygons. This can be changed to any color or weight I want. My original geology unit file has a base color assigned to each unit. When I overlay the pattern files, I can get quite a range of color and pattern combinations, all vectors, so plotting should be no problem, even with a transparent, 2-color DRG bitmapped image.

The files I made in MicroStation are geo-referenced, of course, so they come into MapInfo in a specific place. Rather than make up files for each quad in Oregon, I made a boundary with an "ear" that can be used to drag the patterns around to other quads after they had been imported to MapInfo.

The units for these files are meters, so I would have to make another set of patterns in any other unit I might need to work with, such as feet for state plane coordinates.