A general dynamically consistent 2D flat distribution function is built to model the kinematics of neighbouring stars .
Application leads to the measurement of a short galactic scale length R _ { \rho } between 1.7 and 2.9 kpc and a locally decreasing rotation curve .
This is in agreement with recent determinations based on kinematics and counts of distant stars .
These results rule out the classical assumption that 2 R _ { \rho } = R _ { \sigma } or that \sigma _ { z } ( R ) / \sigma _ { R } ( R ) is constant when the vertical scale height h _ { z } ( R ) is assumed to be constant .
We explain why the measured squared axis ratio of the velocity dispersions \sigma _ { v } ^ { 2 } / \sigma _ { u } ^ { 2 } of disc stars is less than 1 / 2 .
This ratio has been claimed to be important evidence for the non-axisymmetry of the galactic disc .
We show that this is not the case and that it may be simply explained with a realistic axisymmetric disc model if the circular velocity is locally declining or if there is a mismatch between the photometric and kinematic scale lengths .