  We introduce an analytic surface density profile for dark matter halos that
accurately reproduces the structure of simulated halos of mass $M_{\rm vir} =
10^{7-11}\ M_\odot$, making it useful for modeling line-of-sight perturbers in
strong gravitational lensing models. The two-parameter function has an analytic
deflection potential and is more accurate than the projected Navarro, Frenk &
White (NFW) profile commonly adopted at this mass scale for perturbers,
especially at the small radii of most relevant for lensing perturbations. Using
a characteristic radius, $R_{-1}$, where the log slope of surface density is
equal to $-1$, and an associated surface density, $\Sigma_{-1}$, we can
represent the expected lensing signal from line-of-sight halos statistically,
for an ensemble of halo orientations, using a distribution of {\em projected
concentration} parameters, $\mathcal{C}_{\rm vir} := r_{\rm vir}/ R_{-1}$.
Though an individual halo can have a projected concentration that varies with
orientation with respect to the observer, the range of projected concentrations
correlates with the usual three-dimensional halo concentration in a way that
enables ease of use.
