I have a question about about overprinting and its potential use in mapping while working in Illustrator CS3. Traditionally, when creating the linework for roads, we would put the line "fill" in one layer and the line "casing" in another. However, for some of maps my company produces, I notice that overprinting has been turned on for certain layers, specifically those relating to road linework (in these cases, the the Overprint Stroke box in the attribute panel is ticked). The reason why this is an issue is that when we finally print the maps, we get strange results, with the white "fill" not printing at all. For example, instead of getting state roads in the attached image to look like (a), we end up with an image that looks like (. (Please note that the respective layers are set to print and displayed in the final product).
My understanding of overprinting is somewhat nebulous. From what I can gather, it ensures that the blacks contain in different images blend together properly, printing first the CMY colors and then the black over these. However, if this were the case, why would one need to turn on this feature for a white stroke with a 0 K value (such as those dislayed within the picture?). Does not the fact that we have a complex layering scheme render the need for overprinting to be somewhat useless?
Any help would be greatly appreciated!