Context : The understanding of Galaxy evolution can be facilitated by the use of population synthesis models , which allows us to test hypotheses on the star formation history , star evolution , and chemical and dynamical evolution of the Galaxy .

Aims : The new version of the Besançon Galaxy model ( hereafter BGM ) aims to provide a more flexible and powerful tool to investigate the initial mass function ( IMF ) and star formation rate ( SFR ) of the Galactic disc .

Methods : We present a new strategy for the generation of thin disc stars , which assumes the IMF , SFR and evolutionary tracks as free parameters .
We have updated most of the ingredients for the star count production and , for the first time , binary stars are generated in a consistent way .
The local dynamical self-consistency is maintained in this new scheme .
We then compare simulations from the new model with Tycho-2 data and the local luminosity function , as a first test to verify and constrain the new ingredients .
The effects of changing thirteen different ingredients of the model are systematically studied .

Results : For the first time , a full sky comparison is performed between BGM and data .
This strategy allows us to constrain the IMF slope at high masses , which is found to be close to 3.0 and excludes a shallower slope such as Salpeter ’ s one .
The SFR is found decreasing whatever IMF is assumed .
The model is compatible with a local dark matter density of 0.011 M _ { \odot } pc ^ { -3 } implying that there is no compelling evidence for the significant amount of dark matter in the disc .
While the model is fitted to Tycho-2 data , which is a magnitude limited sample with V < 11 , we check that it is still consistent with fainter stars .

Conclusions : The new model constitutes a new basis for further comparisons with large scale surveys and is being prepared to become a powerful tool for the analysis of the Gaia mission data .