Abstract. We discuss star count and three-color data for the two inner-Galaxy fields SA 107 and NGC 6171 observed in the new Basel RGU high-latitude field star survey. Our analysis is based on the structural models of the Galactic population components that were derived from the previous studies of seven fields mainly in the outer Galaxy (Buser et al. 1998, 1999, hereafter Papers I and II, respectively). Apart from the canonical structural parameters, we here explore some of the special conditions prevailing in the transition region from high to low latitudes approaching the Galactic bulge, such as interstellar reddening, preponderant sampling of giants, and possible large-scale radial metallicity gradients. We show that the data are consistent on a high confidence level with a model incorporating an old-thin disk with local mean metallicity These results provide an important further step toward a comprehensive and detailed mapping of the larger-scale density and metallicity structures of the Galaxy, to be derived from the full-survey data in 14 fields.

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A b s t r a c t . A new homogeneous catalog of photographic RGU star count and three-color data in seven high-galactic latitude fields has been used to determine the structural parameter values from a large number of multicomponent population models of the Galaxy. The data provide strong evidence of a prominent thick disk component coexisting with a canonical thin disk and a low-density spheroidal halo.Following the definition and calibration of a standard-RGU system via synthetic photometry techniques [1,2], the plate archive of the BaselPalomar-Schmidt high-latitude survey [3] is being used to construct a homogeneous RGU-photometry data base for a reliable determination of the larger-scale structural parameters and metallicity distributions of the stellar population components of the Galaxy. The new catalog completed to date [4] comprises star counts and three-color distributions for about 1 0 4 stars in seven out of more than a dozen fields of the original survey.We have analysed the data essentially following the methodology developed in [5] and summarized in [2]. For each field, the observed star counts, N (G,G-R)y are compared to the expected counts calculated from each of 12,800 multi-component models of the Galactic stellar distributions, whose parameters are allowed to systematically vary within plausible ranges suggested by previous work. For each model, a ^-estimate of goodness-of-fit to the observed data is computed for each field, whence a global %2-value measuring each model's simultaneous fitting to the all-survey observations in seven fields is derived, and the globally best model is identified by x^t n. Α χ2-curve is then determined for each parameter by allowing it to vary within the adopted range while keeping all other parameters fixed at their 707