Effect of spatial beam (θ_b) and spectral broadening (δV) on peak separation in synthetic transverse PV diagrams for an expanding and rotating annulus of radius r_j and V_ϕ = 3 × V_r. Panel a: significant beam smearing θ_b = 0.2 × r_j but negligible line broadening δV ≪ V_r: peaks on velocity extrema (red dots); this is the case expected for ALMA observations of cool molecular disk winds. Panel b: significant line broadening δV = 0.2× V_ϕ but negligible beam convolution θ_b ≪ r_j: peaks on spatial extrema (blue dots). Panel c: high spatial and velocity resolution (θ_b = 0.1× r_j, δV = 0.1× V_ϕ): peaks between red and blue dots, close to the ellipse major axis; panel d: low spatial and spectral resolution θ_b ∕r_j = δV∕V_ϕ = 1: peaks move closer in, along the ellipse PA.