Sokolowski wrote:Not so sure how to display a lat/lon grid on the main GIS window and on the map composer window ??
This is what, putting a lat/lon grid (graticule) onto a projected map? As Jan suggested, I think you'll have to make your grid using Vector -> Reseach Tools -> Vector grid. Then save it as WGS84 lat/lon (EPSG:4326) and let it reproject on-the-fly in your project. Perhaps it might be preferable to make a polygon grid rather than a line grid, to minimise distortion. I suppose you could also explode a polygon grid to points, in case you wanted to plot the graticule intersections as little crosses.
I haven't tried any of this, mind

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Regards, N.