If a picture is worth a thousand words, a diagram is worth a thousand pictures. Whether you’re presenting a sales strategy to your boss or explaining your newest invention to a friend, diagrams let you express relationships and concepts better than you can with words and images alone. OmniGraffle Professional 4.0, the latest revision of The Omni Group’s diagramming application, adds new features that will entice current users to upgrade and encourage everyone else to take a closer look.

(You may instead choose the Standard edition, which sells for $70 less, and lacks some of the Pro version’s features, including ruler scaling, notes, tables, multi-page documents, and others.)

Layered canvases

OmniGraffle Pro’s main window displays a work area called the canvas, where you lay out the shapes, text, lines, and imported images that make up your diagram.

OmniGraffle Pro lets you build diagrams in two ways. If you prefer to dive right in, you can use its tools to draw geometric or freeform shapes, including Bézier curves, a new feature. Double-clicking a tool in OmniGraffle Pro’s dockable tool palette makes it persist after use, so you don’t have to mouse back to the palette to draw several shapes or lines in succession, for example. For those with less artistic talent, OmniGraffle Pro also provides stencils, libraries of objects suitable for a variety of projects, from business to science.

OmniGraffle Pro’s refurbished inspectors let you adjust the properties of individual elements or the entire canvas. (Click image to open full screenshot)

When you create your diagram, you can set any scale you prefer (1 inch = six feet, say), so it’s easy to accurately portray the dimensions of almost any real-world object (see screenshot). OmniGraffle Pro supports an unlimited number of canvases—when you view a document in Presentation mode, OmniGraffle Pro displays the canvases sequentially, like slides in a PowerPoint or Keynote slideshow. OmniGraffle Pro also lets you define multiple layers on each canvas, a practical way to organize your thoughts when you’re creating a complex diagram.

In the drawer

OmniGraffle Pro’s Utility Drawer, which slides out when you click the Utilities button at the top of the canvas, provides another, more automated route to diagram construction. In addition to the Canvases view, which shows all the canvases and lets you hide or reveal any subset of layers, the drawer includes a view—new in version 4—that displays your diagram in outline form. As you add items to the outline, OmniGraffle Pro assembles the diagram based on a style that you select from a menu at the bottom of the Utility Drawer. OmniGraffle Pro ships with styles for common types of diagrams, and you can define your own styles to add to the basic repertoire.

Lines, magnets, and inspectors

If you’ve ever tried to craft an intricate diagram using a conventional drawing application, you know how difficult it is to prevent all the lines and arrows from becoming a tangled mess of digital spaghetti. When you connect two objects using OmniGraffle Pro’s Line Tool, they remain linked until you sever the tie—as you move the objects around the canvas, the lines move with them. You can even control where the connections terminate by placing virtual “magnets” inside objects.

Like Apple’s Pages (   , April 2005 ) and Keynote (   , April 2005 ), OmniGraffle Pro uses inspectors to centralize most of its formatting and other controls. OmniGraffle Pro 4.0 consolidates the previous version’s multiple inspectors into three vertically arranged panes: Style, Properties, and Canvas. Each pane sports tabs that let you access groups of related functions, such as object and line shadows. A new feature in the Properties pane lets you define pop-up notes that appear when you hover over any item in a diagram for more than an instant.

New on the menu

OmniGraffle Pro 4.0’s beefed-up export functions include improved support for Microsoft Visio files and the ability to export documents in SVG (Scalable Vector Graphics) format. Other new features let you create objects that represent the sum, difference, or intersection of two existing objects, or convert any object on the canvas into a table in which every cell takes on the appearance of the original item.

OmniGraffle Pro isn’t an application that you can expect to learn overnight—mastering its many features takes time and effort. Alas, OmniGraffle Pro’s fragmented documentation makes it difficult for new users to climb its steep learning curve. The information is there, but you’ll have to use the brief manual, on-screen help system, and Web-based guides to find what you need. (Additional samples and walkthroughs should be available online by the time you read this.)

Macworld’s buying advice

While OmniGraffle Professional 4.0 is probably overkill for simple diagrams, this fantastic program is a revelation for anyone who needs to explain processes and concepts visually. If you’re curious, you can download a trial copy from The Omni Group’s Web site. After you play around for a few days, I’m sure you’ll be hooked.

[ Franklin Tessler is a frequent Macworld contributor who uses diagrams for research and teaching. ]