I am going back to re-edit an anniversary ceremony from 2 years ago, and the files are in standard DV NTSC, 4:3, 29.97. The sequence and capture settings match this. When I drag the clips into the viewer, they play full size and unzoomed. When I bring them down to edit in the timeline, they require render, and take up about a quarter of the Canvas window, almost like a video thumbnail sized postage stamp. I have been editing 16:9 HDV recently, but the settings for this project match the original file attributes. What am I doing wrong here? I thought I was past the days when I had to render Standard def DV!

Make the timeline window is active, then push the Command and 0 (zero) keys. This will bring up the sequence settings for the active sequence. Make sure that all the settings are the way they should be.
I have been editing 16:9 HDV recently...
All sequences you create will be defined by your Easy Setup, so if it is set to HDV and you are trying to edit SD, then you will have the problem you describe.

Welcome to DVinfo Kevin! When the settings get messed up I always like to start with a clean slate. Close all projects which are open, go to Easy Setup under the FCP menu and choose DV-NTSC from the dropdown list (assuming that's what you want).

Now start a new project. That will ensure that all new sequences, clips and captures have the correct matching settings. See if that fixes your problem. But note this won't affect any existing sequences or clips, just new ones which you create. If you need to fix an existing sequence then Edward has explained what to do there.