From BlenderWiki

Selecting Faces

Edge selection can be done with simple, “universal” tools described in the basics page. However, when modeling, you will often need some more powerful ways to select your them. One of the most useful one selects faces based on the loops they form. Let’s see this in detail.

Face Loop Selection

In face select mode, holding Alt while selecting an edge selects a loop of faces that are connected in a line end to end, along their opposite edges. In vertex select mode, the same can be accomplished by using CtrlAlt to select an edge ring, which selects the face loop implicitly.

Examples

This face loop was selected by clicking with AltRMB on an edge, in face select mode. The loop extends perpendicular from the edge that was selected.

A face loop can also be selected in Vertex select mode, see (Alt versus CtrlAlt in vertex select mode). The edges selected in the grid labeled “Alt-RMB” is a result of selecting and edge loop versus selecting an edge ring. Because in vertex select mode, selecting opposite edges of a face implicitly selects the entire face, the face loop has been selected implicitly.

Note that in these cases the generated result of the algorithm was vertices because we were in Vertex select mode. However, had we had been in Edge select mode, the generated result would have been selected edges.

Technical Details

The algorithm for selection is as follows:

• A face loop is made by two neighbouring edge loops.
• Extends only to quadrilateral faces.
• Ends when a triangular face is met (and the two bounding edge loops merge into one).

Menu Options

As we saw in advanced selection page, there are some options of the Select menu (3D View header) that specifically concern faces.

For a very mysterious reason, Face Loop does not show itself in this menu…

Face Types

As you might have guessed, these three options allow you to…

• Non-Triangles/Quads (CtrlAlt⇧ Shift3): Select all non-triangle or quad faces (i.e. everything that is not a face).
• Triangles (CtrlAlt⇧ Shift4): Select all triangle faces.
• Quads (CtrlAlt⇧ Shift5): Select all quadrangle and FGon faces.

Note that if the first Non-Triangles/Quads option works in all select modes, the two others are limited to the Face select mode…

Linked Flat Faces

This is an option similar to the Sharp Edges one for edges: it selects all faces linked to those already selected, as long as they are enough “in the same plane” with them. You can enter the limit angle allowed between the faces in the dialog that pops-up when you chose this option.

Note that unlike the Sharp Edges one, this select tool only works in Face select mode. And that here, we select flat faces, so the higher the limit angle, the fewer faces will be selected…