Ionospheric irregularities represent irregular plasma or density variations in the ionosphere and occur predominantly at equatorial latitudes and in aurora/polar regions. Their presence can cause rapid fluctuations in amplitude and phase of Global Navigation Satellite Systems (GNSS) signals, i.e., ionospheric scintillation of GNSS signals. While being affected, GNSS signals provide valuable information on ionospheric irregularities that cause ionospheric scintillations. Recently, a new official ionospheric product to characterize ionospheric irregularities as derived from GPS observations has been released by the International GNSS Service (IGS). This new ionospheric product offered in the format of ionospheric maps is now routinely provided to monitor the high and midlatitude ionosphere of the Northern Hemisphere. With regard to the GNSS-based ionospheric irregularities monitoring over China, this study presents an investigation into ionospheric irregularities mapping by taking advantage of the Crustal Movement Observation Network of China (CMONOC). The CMONOC has been continuously operated for almost two decades since 2000 and now consists of more than 200 GNSS stations. With this dense GNSS network, the rate of change of total electron content index (ROTI) is derived to characterize ionospheric irregularities over the study region. In this study, the ROTI is estimated at different temporal scales, in order to study the impacts of applying GNSS observations at various sampling rates (i.e., 1 sec, 5 sec and 30 sec) on the representation of ionospheric irregularities. The ROTI maps are generated based on the GNSS observations collected over a certain period of interest (e.g., 5 min, 10 min and 30 min) and output in a specific format. Their visualizations are applied to study ionospheric response to several space weather events (e.g., geomagnetic storms). The analysis indicates that the ROTI maps can reveal the temporal and spatial evolution of ionospheric irregularities, which may help warn GNSS users of ionospheric scintillations. It will be developed as one of routine products for real- time ionospheric monitoring at Shanghai Astronomical Observatory.