Mirror Features tool
Kevin, I'm assuming your asking about the Mirror Features editing command, rather than the Mirror—Help | ArcGIS Desktop tool for rasters.
I couldn't find the Mirror Features editing command. john_jones-esristaff is that command around but we're not finding it? Or is there a way to do this?
Kevin, I haven't seen what your features look like, their complexity, the scale at which you're working, etc. Here goes a hare-brained idea that I'll preface with, probably won't work.
Polygon to raster
Mirror
Raster to polygon
Might work for visualization at certain scales (you would definitely need to consider cell size in the first polygon to raster step so that you don't get stepped features later...
Anyway, just trying to think of ways to get you where you're going if there isn't a solid editing workflow in place yet.
I need the Mirror Features tool! I've recently completed the Cartography. MOOC and last week took the Migrating to Pro live-instructor class in Vienna, VA. Both gave me access to Pro (since I do not have it on my machine yet). I looked and looked for this tool, but could not find it anywhere.
My use case: Neighborhood site plans - on a massive scale. Over 4 years, a team of 20+ field data collectors - shot GPS corner points of residential structures, laser-measured the footprints, drew the footprints in CAD, then sent it all back to the office to be imported into GIS where we snapped the footprints to the GPS points.
In neighborhoods where floor plan models repeated (extremely common), the team would measure the building-type once and then direct the office team to Mirror the footprint. The GIS technicians would create a bank of Footprints with a Standard and Mirrored version of each - and then follow the directive of the field team to know which footprint went to each set of GPS points. This 2-second mirroring operation saves hours of time over the life of a project such as this.
To add this in Desktop was simple - add the Editor toolbar (it's the most obvious place to place the button). Rt click as if to add another toolbar --> scroll down to the bottom to Customize --> Open Commands tab --> Search by "Mirror" --> Choose the Editor version (the icon with two triangles separated by a line and an arrow from one triangle to the other). Drag the icon to the Editor toolbar. Voila! Now mirroring a polygon, line work or a group of points is as simple as selecting the objects and drawing a 'flip line'. The selected items appear on the other side of the flip line. 