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How are quasars represented in specialized astronomical maps?

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Astronomical map Star trails over banksia trees, in Gippsland, Vic., Austl. The south celestial pole, located in the constellation Octans, is at the centre of the trails.

In specialized astronomical maps and surveys, quasars are typically identified and represented based on their unique observational characteristics rather than a single standardized symbol. Because they appear as starlike, point-source objects in optical images, they are often distinguished from normal stars through the following methods:

Color Selection: Quasars are frequently isolated by their unusually blue color compared to typical stars. Astronomers use multiple filters to photograph large areas of the sky, comparing the brightness of objects across different wavelengths to identify these blue sources.12
Spectroscopic Verification: Once a candidate is identified on a map, its nature is verified through spectroscopy. This process reveals characteristic emission lines that are significantly redshifted, confirming the object's extreme distance and high luminosity.123
Multi-wavelength Indicators: Maps may also incorporate data from X-ray surveys or infrared observations. High levels of X-ray emission are considered a reliable indicator of the accreting black-hole systems that power these active galactic nuclei.14

While they were originally discovered as "quasi-stellar radio sources" in early radio surveys, modern mapping techniques rely on these combined photometric and spectroscopic signatures to distinguish them from the surrounding galactic population.142