The choice of scale for summarizing data
Authors: Yiyi Zhang, Hugo Thierry, Peter Rodriguez
Introduction
We often report data by summarizing fine-scale information (e.g., at a pixel) to coarse-scale analysis or reporting units (e.g., census division). In this example, we discuss this challenge known as Modifiable Areal Unit Problem (MAUP) and how it may visually bias our understanding of ecosystem service supply and demand relationships.
Case study
Pollination is beneficial to the production of certain crops such as soybean and fruit trees. Landscape areas with more nesting and floral resources are pollinator-suitable habitats. Pollinators such as bumble bees can fly from their habitats to nearby (~1.5km) crop fields and provide pollination service [23]. We summarize pollinator abundance index estimated using InVEST model, and pollination demand estimated based on the area of pollinator-dependent crops into 3km cells that can better capture effective pollination. We also summarize the information into the watersheds, which is a common scale for governance activities, to compare supply-demand relationships.
In the figure below, areas with no demand are observed in panel a, but not in panel b. In panel a, most cells show high demand-low supply relationship, while in panel b, most watersheds show more balanced high demand-high supply relationship. Cells with low demand and high supply tend to be in watersheds with the same relationship. When making decisions among the watersheds, areas that could benefit from improved effective pollination supply (e.g., cells with high demand and low supply) may not be evident at the watershed-level results.
Best practices and opportunities
-
Choose a reporting unit based on the research question or management context. If these are not clear, assess and report the results from a range of scales and assess the representativeness of the assessed relationship. For example, it is recommended to quantify the percentage of outcome agreement and disagreement between scales, such as supply-demand relationship between cells and watersheds discussed in the case study.
-
Addressing MAUP provides an opportunity to identify most suitable units for the accounting of various ecosystem assets and ecosystem services, given scale-dependent relationships between ecological functions and social activities.