Radial distribution of the mean metallicity of the entire stellar population. Observations obtained from the photometric analysis of colour-maginitude diagrams (CMD, Gogarten et al. 2010) are shown as red circles and the Model B prediction is displayed as the black solid line. The Model B predicted metallicity of the ISM and the very young stars is additionally shown as the red dashed curve. For comparison purposes, the blue dotted curve represents the black curve shifted by +0.24 dex.