Projected spatial distribution onto the Galactic plane of SNRs in the three samples analyzed here with distances taken from Ranasinghe & Leahy (2022) and coloured according to log(ν_∗/MHz) using the colour bar code. Filled symbols show the location of SNRs with turnover spectra, while the open symbols indicate those sources not showing turnovers. Circles correspond to Castelletti et al. (2021) plus this work data, squares correspond to Kovalenko et al. (1994b), and triangles to Kassim (1989). As a guidance the solid black lines show the position of the spiral arms taken from the Hou & Han (2014) model. The central plus symbol indicates the position of the Galactic centre, the solar symbol shows the Sun’s position, and the dotted lines the Galactic quadrants. The coloured points do not show any strong dependence on heliocentric distance or Galactic longitude (see Figs. 10 and 11).