This work presents an analysis of some standard methodologies for positional accuracy assessment of geographic data bases, taking into account aspects like the statistical formulation, the size of the control sample, the distribution and typology of the control elements, etc. Here we point out some weaknesses of the majority of standards: scarce formalism, inappropriate terminology for dealing with uncertainty, minimum recommended sample size, no assessment of the base hypothesis of the statistical model being applied, no information about the statistical behavior and reliability of the method, etc. The analysis developed here can serve as a starting point for the development of improved methodologies.

The Roman bridge of Alcántara is the largest in Spain. Its preservation is of the utmost importance and to this end different aspects must be studied. The most prominent is the assessment of its structure, and this is especially important as the bridge remains in use. This paper documents the way the assessment of structural safety was carried out. The assessment methodology of existing structures was applied. The preliminary assessment was based on bibliographic data and non-destructive techniques. The geometric data of the bridge were obtained by Terrestrial Laser Scanning (TLS), which made possible the analysis of its deformations and assessment of its structure. Ground-Penetrating Radar (GPR) was also used with different antennae to work at different depths and spatial resolutions with the aim of analysing structural elements. From the above information, the assessment of structural safety was made using the limit analysis method by applying the historical works carried out on it and those described in the regulation of obligatory compliance in Spain (IAP11), studying the sensitivity of safety to the most relevant parameters. The state of preservation and structural integrity of the bridge is discussed and conclusions are drawn on the areas of greatest risk and the bases for the following assessment phase of preservation of the bridge.

A simulation process is implemented in order to generate synthetic populations of positional-planimetric errors and later, by a bootstrap process, a family of acceptance curves (nomogram) has been derived. These curves allow us to learn the acceptance level, or pass level, of a geographic database when a positional control test based on bias and on variability is applied to it against a given standard. Acceptance curves allow us to report user’s risk and to determine the adequate size of the sample in order to reduce this risk to a desired level.

Gully erosion in agrosilvopastoral systems of SW Spain represents a common degradation process, but has been hardly analysed. The suitability of using the Unmanned Aerial Vehicles (UAV) and Structure from Motion photogrammetry (SfM) workflow to map small valley-bottom gullies in these landscapes was tested. The results showed centimetre-level accuracy. Observed strengths and limitations of the UAV+SfM workflow in the study areas are discussed. The resulting cartography allowed mapping soil erosion forms at outstanding spatial scales. All study areas showed evidences of degradation.

Using a statistical simulation process the variability of National standard for spatial data accuracy (NSSDA) estimations are analyzed according to sample size. Simulation results show: (1) that the NSSDA positional accuracy estimation has a variability of 11% when using the minimum recommended sample size of 20 points; and (2) that the use of samples of 100 points is needed in order to reach an effective confidence level of 95%. The NSSDA is a methodology of shared risk between users and producers when accuracy is “as expected,” but for other cases the relation is altered. As simulation results demonstrated, this change is depicted by means of a family of acceptance curves that can be used by users to determine the sample size for limiting their acceptance risk, but also by producers to analyze their rejection risk.