Use ERDAS IMAGINE to create and output a variety of types of hard-copy maps, with several referencing features.
A scaled map is a georeferenced map that has been projected to a map projection, and is accurately laid-out and referenced to represent distances and locations. A scaled map usually has a legend, that includes a scale, such as 1 inch = 1000 feet. The scale is often expressed as a ratio, like 1:12,000, where 1 inch on the map represents 12,000 inches on the ground.
Printing Large Maps
Some scaled maps do not fit on the paper that is used by the printer. These methods are used to print and store large maps:
- A book map is laid out like the pages of a book. Each page fits on the paper used by the printer. There is a border, but no tick marks on every page.
- A paneled map is designed to be spliced together into a large paper map; therefore, borders and tick marks appear on the outer edges of the large map.
Layout for a Book Map and a Paneled Map
Scale and Resolution
The following scales and resolutions are noticeable during the process of creating a map composition and sending the composition to a hard-copy device:
- spatial resolution of the image
- display scale of the map composition
- map scale of the image or images
- map composition to paper scale
- device resolution
Spatial resolution is the area on the ground represented by each raw image data pixel.
Display scale is the distance on the screen as related to one unit on paper. For example, if the map composition is 24 inches by 36 inches, it would not be possible to view the entire composition on the screen. Therefore, the scale could be set to 1:0.25 so that the entire map composition would be in view.
The map scale is the distance on a map as related to the true distance on the ground, or the area that one pixel represents measured in map units. The map scale is defined when you create an image area in the map composition. One map composition can have multiple image areas set at different scales. These areas may need to be shown at different scales for different applications.
Map Composition to Paper Scale
This scale is the original size of the map composition as related to the desired output size on paper.
The number of dots that are printed per unit—for example, 300 dots per inch (DPI).
Use ERDAS IMAGINE Map View to define the above scales and resolutions.
Map Scaling Examples
Define a map size using the ERDAS IMAGINE Map View, as well as define the size and scale for the image area within the map composition. The examples focus on the relationship between these factors and the output file created by Map View for the specific hard-copy device or file format. The figure below is the map composition that is used in the examples. This composition was originally created using the ERDAS IMAGINE Map View at a size of 22" × 34", and the hard-copy output must be in two different formats.
- It must be output to a PostScript printer on an 8.5" × 11" piece of paper.
- A TIFF file must be created and sent to a film recorder having a 1,000 dpi resolution.
Sample Map Composition
Output to PostScript Printer
Since the map was created at 22" × 34", the map composition to paper scale needs to be calculated so that the composition fits on an 8.5" × 11" sheet of paper. If this scale is set for a one to one ratio, then the composition is paneled.
To determine the map composition to paper scale factor, first calculate the most limiting direction. Since the printable area for the printer is approximately 8.1" × 8.6", these numbers are used in the calculation.
- 8.1" / 22" = 0.36 (horizontal direction)
- 8.6" / 34" = 0.23 (vertical direction)
The vertical direction is the most limiting; therefore, the map composition to paper scale would be set to 0.23.
Use Print Map Composition dialog to output a map composition to a PostScript printer.
If the specified size of the map (width and height) is greater than the printable area for the printer, the output hard-copy map is paneled.
See the hard-copy device manual for printable area information.
Output to TIFF
The limiting factor in this example is not page size, but disk space (600 MB total). A three-band image file must be created in order to convert the map composition to .tif file. Due to the three bands and the high resolution, the image file could be very large. The .tif file is output to a film recorder with a 1,000 DPI device resolution.
To determine the number of megabytes for the map composition, the X and Y dimensions need to be calculated:
- X = 22 inches × 1,000 dots/inch = 22,000
- Y = 34 × 1,000 = 34,000
- 22,000 × 34,000 × 3 = 2244 MB (multiplied by 3 since there are 3 bands)
Although this appears to be an unmanageable file size, it is possible to reduce the file size with little image degradation. The image file created from the map composition must be less than half to accommodate the .tif file, because the total disk space is only 600 megabytes. Dividing the map composition by three in both X and Y directions (2,244 MB / 3 /3) results in approximately a 250 megabyte file. This file size is small enough to process and leaves enough room for the image to TIFF conversion. This division is accomplished by specifying a 1/3 or 0.333 map composition to paper scale when outputting the map composition to an image file.
Once the image file is created and exported to TIFF format, it can be sent to a film recorder that accepts .tif files. Remember, the file must be enlarged three times to compensate for the reduction during the image file creation.
Use Print Map Composition dialog to output a map composition to an image file.
See the hard-copy device manual for DPI device resolution.