On the impact of geospatial features in real estate appraisal with interpretable algorithms

Abstract: Real estate appraisal is the means of defining the market value of land and property affixed to it. Many different features determine the market value of a property. For example, the distance to the nearest park or the travel time to the central business district may be significant when determining its market value. The use of machine learning in real estate appraisal requires algorithm accuracy and interpretability. Related research often defines these two properties as a trade-off and suggests that more complex algorithms may outperform intrinsically interpretable algorithms. This study tests these claims by examining the impact of geospatial features on interpretable algorithms in real estate appraisal. The experiments use property transactions from Oslo, Norway, and adds relative and global geospatial features for all properties using geocoding and spherical distance calculations. Such as the distance to the nearest park or the city center. The experiment implements three intrinsically interpretable algorithms; a linear regression algorithm, a decision tree algorithm, and a RuleFit algorithm. For comparison, it also implements two artificial neural network algorithms as a baseline. This study measures the impact of geospatial features using the algorithm performance by the coefficient of determination and the mean absolute error for the algorithm without and with geospatial features. Then, the individual impact of each geospatial feature is measured using four feature importance measures; mean decrease impurity, input variable importance, mean decrease accuracy, and Shapley values. The statistically significant results show that geospatial features improve algorithm performance. The improvement of algorithm performance is not unique to interpretable algorithms but occurs for all algorithms. Furthermore, it shows that interpretable algorithms are not axiomatically inferior to the tested artificial neural network algorithms. The distance to the city center and a nearby hospital are, on average, the most important geospatial features. While important for algorithm performance, precisely what the geospatial features capture remains for future examination.