In this paper, we propose a method to estimate an adaptability of environmental data on each farmland concerning with each cultivation of vegetables. We propose an actual method to represent a feature of a farmland. We define an adaptability of a farmland for vegetables as a value of differences between environmental data on the farmland and a condition of a standard manner of the cultivation. Since the size of observed data on each farmland is big, it is difficult to apply various algorithms for analysis to the data. Therefore, we present the method to compress such a big data into a simple value by indexing from observed values into-1, 0, or 1. Then, the method is applied to the data obtained by our cultivation experiment of tomatoes. From the result by comparing the values of adaptability obtained by experiments in 2013 and 2014, we show that the adaptability can be expected to have close relationship with growth of vegetables.