Abstract
Abstract: In many countries, the positional accuracy control by points in Cartography or Spatial data corresponds to the comparison between sets of coordinates of well-defined points in relation to the same set of points from a more accurate source. Usually, each country determines a maximum number of points which could present error values above a pre-established threshold. In many cases, the standards define the sample size as 20 points, with no more consideration, and fix this threshold in 10% of the sample. However, the sampling dimension (n), considering the statistical risk, especially when the percentages of outliers are around 10%, can lead to a producer risk (to reject a good map) and a user risk (to accept a bad map). This article analyzes this issue and allows defining the sampling dimension considering the risk of the producer and of the user. As a tool, a program developed by us allows defining the sample size according to the risk that the producer / user can or wants to assume. This analysis uses 600 control points, each of them with a known error. We performed the simulations with a sample size of 20 points (n) and calculate the associated risk. Then we changed the value of (n), using smaller and larger sizes, calculating for each situation the associated risk both for the user and for the producer. The computer program developed draws the operational curves or risk curves, which considers three parameters: the number of control points; the number of iterations to create the curves; and the percentage of control points above the threshold, that can be the Brazilian standard or other parameters from different countries. Several graphs and tables are presented which were created with different parameters, leading to a better decision both for the user and for the producer, as well as to open possibilities for other simulations and researches in the future.
Highlights
The normative, in the area of this paper, for the major of the countries currently has its conceptual base on the ISO standards by considering the geospatial control quality, which includes the ISO series (1985, 1995, 1999, 2002, 2003a, 2003b, 2005, 2006, 2007, 2013, 2014)
The general aim of this paper is to present a computer program that was developed for spatial data quality control analysis and the construction of operational curves to help users to define the size of the sample related to the risk a user or a producer is willing to take
A great advantage of the program is that it allows a remarkable flexibility for the parameters input and can be applied to most countries, aiming at the punctual positional control quality of maps or at any other spatial dataset, making the appropriate adaptations
Summary
The normative, in the area of this paper (positional accuracy of spatial data), for the major of the countries currently has its conceptual base on the ISO standards by considering the geospatial control quality, which includes the ISO series (1985, 1995, 1999, 2002, 2003a, 2003b, 2005, 2006, 2007, 2013, 2014). The general aim of this paper is to present a computer program that was developed for spatial data (maps and others) quality control analysis and the construction of operational curves to help users to define the size of the sample related to the risk a user or a producer is willing to take. This risk is associated with the standard of each country; the program allows introducing the adequate parameters for the calculations
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