  Interacting two-dimensional electrons confined in a GaAs quantum well exhibit
isotropic transport when the Fermi level resides in the first excited ($N=1$)
Landau level. Adding an in-plane magnetic field ($B_{||}$) typically leads to
an anisotropic, stripe-like (nematic) phase of electrons with the stripes
oriented perpendicular to the $B_{||}$ direction. Our experimental data reveal
how a periodic density modulation, induced by a surface strain grating from
strips of negative electron-beam resist, competes against the $B_{||}$-induced
orientational order of the stripe phase. Even a minute ($<0.25\%$) density
modulation is sufficient to reorient the stripes along the direction of the
surface grating.
