About 10 years ago, when working freelance, I produced some diagrams which mapped LaTeX page layout parameters to the equivalent descriptions used by regular book designers. I’ve redrawn everything into SVG using the excellent open-source vector drawing software Inkscape. I’ve uploaded the resulting diagram here in advance of writing a tutorial to explain everything in a bit more detail, including a simple Lua script for use with LuaTeX. Please note that I have only tested viewing the SVG via FireFox (3.6.13 on Windows). Apologies if it does not work for you, feel free to download the diagram and view it offline. In the meantime, I hope you find it useful — I have switched on comments for this post, in case anyone happens to spot an error and would be kind enough to let me know.