Operating for more than 3 Mars years, the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has provided a unique opportunity to study the variability of the Martian upper atmosphere and ionosphere and their interaction with the solar wind under various conditions. This work presents the observed dayside ionosphere using the Neutral Gas and Ion Mass Spectrometer (NGIMS) measurements. NGIMS is a mass spectrometer onboard the MAVEN spacecraft with open or closed sources, where ions from one source are measured by a quadrupole mass filter that allows only ions of a selected mass to charge to be counted by a detector. NGIMS measures the composition and structure of the ions and neutrals in the ionosphere and thermosphere at altitudes below ~500 km. Here, we present what 3 Mars years of the MAVEN measurements allow us to see: 1) the spatial and compositional variations of the average ionosphere, 2) the observed ionospheric peak layer (M2 layer) at high solar zenith angles (SZAs), which compliments the observations by the previous missions at lower SZAs, and 3) the observed seasonal variability of the ionosphere.