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The century-long (1907-2007) Ca II K spectroheliograms from Kodaikanal SolarObservatory (KSO) are calibrated, processed and analysed in the present studyto follow the evolution of bright on disc structures called plages, thepossible representatives of magnetic activity on the Sun. This has been thelongest dataset studied in Ca II K till date covering about 9.5 cycles of 11year periods. Plages were segmented with area $\geq 1\:\textrm {arcmin}^2$using global thresholds for individual full disc images and subsequentapplication of morphological closing operation. Plage index was calculated andseen to have close positive correlation with fractional disc area covered byplages. The newly generated plage area cycle (from KSO) was compared with thesame from Mount Wilson observatory (Correlation~$95.6\%$) for the overlappingyears i.e. 1915-2000. Study illustrated time-latitude distribution of plagecentroids rendering butterfly diagram (as observed for sunspots). The 3Dvisualisation of the diagram showed one to one mapping between plage location,time and area. This work further delineated positional correlation betweenmagnetic patches and plage regions through comparison of synoptic maps derivedfrom both Kodaikanal Ca II K images and space based full disc LOS (line ofsight) magnetograms. Regular synoptic magnetograms from ground basedobservatories are available only after 1970s. Thus the long term Ca II K datafrom KSO can be used as a proxy for estimating magnetic activity locations andtheir strengths at earlier times.

Butterfly Diagram and Carrington Maps for Century-Long Ca II K Spectroheliograms from Kodaikanal Observatory