Producing a map may require several different types of tools and processes, depending on whether you are creating a printed or electronic map. In this part of the lesson, we will think about the map production process in both generic and specific terms. First, we will talk about some pieces of equipment that may be needed regardless of the media you choose to work in, and then we will talk about some specific requirements for particular end products.
It may be helpful to organize our discussion by thinking about a typical workflow that you might use when producing a map. Figure 1.11.1 outlines the basic steps in producing a map.
Data compilation involves gathering and collecting any spatial and/or attribute data that you will need for creating your map. In some cases, the data that you will need for the particular map you want to create will already exist in a digital format that can be directly imported into a GIS. Your own organization may have already collected the data, or they may have been created by a government agency, non-profit organization or private firm. In other cases, the data you would like to use may exist, but are in an analog rather than digital format. In this situation, you can often use a digitizing tablet or a scanner (see Figure 1.11.2) to transform the data into a format that a GIS can use. Although an immense amount of digital geospatial data already exists, you may still find yourself in the position of having to create your own data, either because no one has already collected it or because the available data is not suitable for your purposes (e.g. a civil engineering firm will most likely need more precise elevation data for planning road grades than what they can extract from a 30 meter resolution DEM). In this case, you may need to use surveying equipment or a GPS receiver (see Figure 1.11.3). The compilation process is largely independent of the final map media.
The second step in the map production workflow is the actual designing of the map. Most computer-assisted map production used to be done with graphics illustration software. However, the cartographic tools in GIS software packages have gradually been improving. It is now possible (in at least some software packages) to create all of the components needed for offset printing within the GIS software. Some examples of GIS software packages you might use for map production include: ArcGIS, MapInfo, IDRISI, Intergraph Geomedia, and Autodesk Map.
Although the cartographic tools embedded within GIS software have been improving, you may find that there are some operations that you either just cannot perform in the GIS, or that are tedious and cumbersome in this software environment. Often, cartographers turn to graphic design software for more sophisticated functionality and more precise control over graphic elements. Graphic design software falls into three major categories: illustration software, image-editing software, and page-layout software. Illustration software is vector based (i.e. the file contains objects such as points, lines and polygons that you can manipulate (see a more detailed discussion of vector and raster in Part VII: Objects vs. Fields). Some of the more popular packages include Adobe Illustrator, Macromedia Freehand, and CorelDRAW. Image-editing software, on the other hand, is raster based (i.e. it is pixel-based rather than object based). Cartographers often use image-editors such as Adobe Photoshop, Corel Painter, or Paintshop Pro to further enhance shaded relief in their maps. Page-layout software—such as QuarkXPress, Corel Ventura, and Adobe InDesign (formelry known as PageMaker)—combines both the vector and raster graphics handling capabilities of illustration and image-editing software packages.
The final step in the map production process is in creating the final output. The equipment you will need for this step will depend upon the final production media used for publication. Here, we will consider two classes of media: print and electronic.
Maps published in electronic media (see more on this in Part VI: Print and Electronic Media) are typically displayed on either a computer screen, television screen, computer projector or some type of hand-held electronic device (e.g. PDA, cell phone, etc.). Oftentimes, the design challenges you will face will be specific to the particular electronic display device, so it's important to find out as much as you can about the final output device(s). For example, a cell phone screen may be limited both by the size of the display and whether it is black and white or color. A map displayed on a television news program may face the limitations of (relatively) poor screen resolution and short viewing time. There can even be significant differences between computer monitors: liquid crystal display (LCD) screens (e.g. laptop screens or the new flat-panel monitors) tend to wash out colors as compared to more traditional cathode ray tube (CRT) computer monitors (see Figure 1.11.4).
Maps published in print media fall into two general classes: maps printed on inkjet printers, laser printers or plotters (i.e. personal printers), and maps that are professionally printed on offset printing presses. If you only need to produce a small number of copies of your map, it's likely that you will choose to use a personal printer, as it is much quicker and cheaper than having the maps professionally printed. Inkjet printers are typically the most affordable option, but they print at a lower resolution than a laser printer, so you sacrifice print quality for cheaper production. Laser printers, which are now available for both black and white and color printing, print at a higher resolution, but are typically 3-4 times more expensive to purchase, and the cost of ink is also higher. Plotters are most useful for producing small quantities of large-format (greater than 11x17") maps (see Figure 1.12.5).
If you need to produce large numbers of a map, or if your map needs high quality printing (e.g. if you need to use very small type or very fine lines), you will probably have your map professionally printed on an offset printer. Although the cartographic design process is the same, regardless of how the final map is printed, offset printing requires a number of additional processing steps, collectively known as pre-press operations. Figure 1.12.6 outlines the basic steps involved in pre-press map production.
As you can see in the figure above, the first step in this workflow is creating a digital positive image. This stage is the equivalent to the output stage in Figure 1.11.1, the general map production workflow. At this point, you have a file that has either been created with a GIS or with a combination of a GIS and graphic design software.
Although offset printing can be done in black-and-white, most cartographers who go through the trouble of having their maps professionally printed are working with color. There are two main types of color printing: process color and spot color. Process color printing allows the designer to choose and use a full range of color hues. This process involves passing the map through the printing press four times, each time printing with varying amounts of one of four colors of ink: cyan, magenta, yellow and black. We will talk about this type of color in more detail in Part X: Color Spaces and Color Specifications. Spot color printing is a type of printing that cartographers and designers use when they either want to include some color in their maps but do not need (or cannot afford) a full range of colors, or when the color the cartographer would like to use is difficult or impossible to create using process colors. Spot colors (also called custom colors), are premixed inks that are used instead of or in addition to the four process colors.
Regardless of the type of color you use for your map, printing in more than one color requires the preparation of color separations (see Figure 1.11.7). Color separations are a way to decompose the parts of a full color image into the four process colors. For example, to create a particular shade of orange, you need to mix some amount of magenta ink with some amount of yellow ink. Creating a color separation specifies the amount of each ink color that gets printed on the page. Color separations can also be used to specify where spot colors get printed within an image. All graphic design software packages (and some GIS software packages) have functionality that allows you create color separations. Personal printers perform color separations internally, so this step is only needed if you are having your maps printed on an offset press.
After you have created the necessary color separations, you need to produce a negative for each separation that can then be used to create a printing plate. In the days of manual cartography, this negative was prepared photographically from a positive image, using a process camera (you may have heard the term "camera-ready artwork") (see Figure 1.11.8). Today, negatives can be directly created with an imagesetter, a machine that uses raster image processing (RIP), the same technology that drives personal printers, to produce very high resolution images (up to 2,400 dpi). Once you've created a negative, it is important to generate a pre-press proof (see Figure 1.11.9). A pre-press proof is an image that gives a close approximation of what the printed image will look like. It allows you to check the map one more time for errors and to ensure that the colors look correct. After proofing, the printer proceeds to make a printing plate using a platemaking machine. This machine exposes the photoreactive printing plate and the negative to an intense light source, creating a positive or "right-reading" plate for use with the printing press. One relatively new technology, the direct to plate (DTP) system now allows cartographers to print to an offset printer without making film negatives. With this technology, the printing press is connected to a DTP system. The system allows the printer to create color-separated plates by using the RIP software to drive a laser that directly transfers the image onto a plate inside the press. By eliminating the need for negatives, DTP increases the printer's efficiency. One disadvantage of the DTP system, however, is that it does not produce a color proof, so errors can only be caught after printing has begun.
The final step is the actual printing. As its name implies, in offset printing, the printing plate does not actually come into contact with the paper. Rather, ink is transferred from the plate onto a rubber blanket which is used to transfer the ink onto the paper (see Figures 1.12.10 and 1.12.11). One of the main advances of offset printing is that it allowed designers and cartographers to create "right-reading" originals.