1 INTRODUCTION  
2 SAMPLE AND DATA  
2.1 The CALIFA survey  
2.2 The EDGE survey  
3 ANALYSIS  
3.1 CALIFA and EDGE Spatially Resolved Properties  
4 RESULTS  
4.1 Global Properties  
4.2 Radial binned properties  
4.3 Spaxel-by-spaxel Properties  
4.4 The impact of EW(Hα) on the resolved Σ_gas - A_V relation  
4.5 Validation of dust-inferred gas masses  
4.6 Caveats  
5 DISCUSSION  
5.1 Previous CO and optical extinction measurements  
5.2 The physical interpretation of the scatter of the gas-extinction relation  
5.3 The impact of metallicity on the gas-extinction relation  
5.4 Scaling relations using the Gas-Extinction calibrator  
6 SUMMARY AND CONCLUSIONS