1. Introduction

2. Spectroscopic surveys
2.1. APOGEE
2.2. RAVE
2.3. GES
2.4. LAMOST

3. Comparison of stellar parameters between the surveys

4. Common fields and distance determination

5. MOCK fields using stellar population synthesis models
5.1. Applying uncertainties and related checks on the models
5.2. Comparison between GALAXIA and TRILEGAL
5.3. Effects of the selection function in MDF

6. Vertical metallicity gradients in ALR and AGR
6.1. Effects of selection function in vertical metallicity gradients
6.2. Vertical metallicity gradients for the observed sample

7. Conclusions