We investigate metallicity and {alpha}-element abundance gradients along a Galactic longitude strip, at latitude b~-4{deg}, with the aim of providing observational constraints for the structure and origin of the Milky Way bulge. High-resolution (R~22500) spectra for 400 Kgiants, in four fields within -4.8{deg}<~b<~-3.4{deg} and -10{deg}<~l<~+10{deg}, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another ~400 stars in Baade's Window at (l,b)=(1{deg},-4{deg}), observed with the identical instrumental configuration: FLAMES GIRAFFE in Medusa mode with HR13 setup. All target stars lie within the red clump of the bulge colour-magnitude diagram, thus minimising contamination from the disc or halo stars. The spectroscopic stellar surface parameters were derived with an automatic method based on the GALA code, while the [Ca/Fe] and [Mg/Fe] abundances as a function of [Fe/H] were derived through a comparison with the synthetic spectra using MOOG. We constructed the metallicity distributions for the entire sample, and for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions.