Illustration of source types in the classification process of Sect. 3.6. From top to bottom: typical multiband images of a radio source classified as an H II region, a planetary nebula, a radio star and a extragalactic source. From left to right: three-colors composition image of UKIDSS (red = 2.2 µm, green = 1.65 µm, blue = 1.2 µm), three-color composition image of GLIMPSE (red = 8 µm, green = 4.5 µm, blue = 3.6 µm), three-color composition of WISE (red = 22 µm, green = 12 µm, blue = 4.6 µm), MIPSGAL 24 µm, Hi-GAL 70 µm, Hi-GAL 160 µm, Hi-GAL 250 µm, Hi-GAL 500 µm, and ATLASGAL 870 µm. The blue and white circle in the center show the position of radio emission. The FWHM beams of UKIDSS (0.8″), GLIMPSE (2″), WISE (6″ at 12 µm), MIPSGAL (6″ at 24 µm), Hi-GAL (6″–35″), ATLASGAL (19″) are indicated by the white circles with black hatched lines shown in the lower-left corner of each image.