Where 2 polygons are adjacent to each other this sort of misregistration can lead to a gap between the colors, or a dark line if the inks overlap.

‘Pre-Press’ includes a fix for this - a ‘Trapping’ routine is applied to the image. A thin line in a neutral color is generated along the edge of each polygon or line to provide a ‘cushion’.

However, this can create a problem for detailed maps, where very thin lines are common. Trapping tends to thicken the line, sometimes unacceptably so. Here are 3 ways to sidestep the issue:

• Use single printing colors for thin lines.

• Limit the line to 2 printing colors, then build in an overlap. This gives you control of the thickness of the line.

• Use an 'overprint' setting

Overprint sidesteps the issue you face with adjacent features, but at a cost.

Imagine you have a single-line water course running over a polygon (common enough on a map).

A misregistration of the magenta could look like this:

Overprint retains the other components of a color behind the line. Where the two overlap the magenta and yellow components of the background are added to the water course:

In this example the river turns darker, but it looks better (sharper) than the knocked-out setting, despite the misregistration.

A combination of these techniques will counter most misregistration issues, limiting the need for automatic trapping.

Note that, unless told differently, a printer will usually set an automatic overprint on 100% black. This means that, at the very least, much of the map labelling will be sharp and clear. If there is a reason why this may cause problems, you should talk to the printer.

These days your deliverable to the Printer will be a digital file, most likely in PDF format. If the final product is in book form, Pre Press will take that file and create an image of 8/16/32 pages called a Signature (or Section). The pages will be distributed in such a way that the flat sheet can be folded to place all of the pages in the correct sequence.

This image will be transferred to the press.

The type of press used will be governed by the type of product and the size of the print run:

• A very short print run may go on an 'On-Demand' digital press. The mis-registration problems I discuss above may not apply, but it's only economic for single copies or short runs.

• A large flat map, a print run of a few thousand, or a high quality product may run on a sheet-fed press. Here, single sheets of paper feed into the press and output as single sheets. Any folding and trimming is handled after the fact.

• A large print run may go on a web press. Here a continuous roll of paper feeds into the press. After printing, the roll continues into a folding machine where the signatures are separated, and folded.

Depending on how invested you are in the production process, you may be asked to go on a press check. This means that you will attend the print run to explain any specific requirements the pressmen need to know, and to review and sign-off on the final print as it comes off the press. You will be looking at the quality of the color, the standard of registration, and anything else that might affect the appearance of the final product.

With a sheet-fed press this may be fairly relaxed. Sheets will be run, then the press will stop, and a sample will be brought over to you (sometimes in another room). Your comments will be relayed back to the pressmen, who will make adjustments then return another copy. When you are satisfied with the result, you will be asked to sign the sheet, and this will be used as the model going forward.

With a web press this can be high pressure! Once it is running, the press won't stop until the print run is complete. You make your assessments while printed product is coming off the press and straight into a dumpster. The printers will build-in a cushion when they set up the press to allow for this process, but you need to be conscious of how much paper has gone through, and what the costs will be if the roll runs out. You will need to learn what is an acceptable result for this process rather than looking for perfection.

Once you sign-off on the result, the press will go up to full speed and the printed product will be saved.

Once a map or book has gone to press there is no easy way of correcting mistakes, and a reprint may involve significant cost. For this reason a thorough editing stage is a must before a product is released.

Having said that, mistakes do happen, and anyone who has been in this business will have a fund of stories about them (I won't include any here, but ask me if you want to know more!)

This is the fourth of a series of 'How to' Stories looking at the ways I develop my work. The other sections are:

  Planning and Executing a Map Project  

  Working with Color  

 Building Maps for Vision deficiency 

 Working for Print in ArcGIS 

Andy Skinner, 2024