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title: "tab5_spatial"
output: html_document
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### **Module:** ***Spatial Partition***

**BACKGROUND**

Spatial partitions have important advantages over non-spatial ones when sampling bias is known or suspected, and when the application will require transfer across space and/or time.

**IMPLEMENTATION**

This module implements functionalities from the R package `ENMeval` to partition the occurrence localities into training and testing datasets. 

The user can choose one of three means of spatial partitioning: the 1) “block”, 2) “checkerboard 1”, or 3) “checkerboard 2” options. The “block” method draws a latitudinal and then a longitudinal line to create four groups of localities corresponding to spatial rectangles (*k* = 4). These rectangles hold similar numbers of localities but typically differ in area. The “checkerboard 1” method breaks the extent into a checkerboard pattern and attributes localities to one of two groups depending on which square they fall in (*k* = 2). The “checkerboard 2” method is similar, but adds another level of hierarchy to the spatial grouping, resulting in *k* = 4 groups. Specifically, a coarser checkerboard is placed on top of “checkerboard 1” with grid size equal to a user-specified “aggregation factor” that is multiplied by the length of the finer grid. Later versions of *Wallace* may include other varieties, such as more sophisticated nearest neighbor approaches to partitioning. For more details about these partitioning methods, see Muscarella et al. (2014). Users can download a .csv that includes all the localities retained thus far with an extra column for partition group, plus all the background points sampled in Component **Process Environmental Data** (partition value = 0).

**REFERENCES**

Muscarella R., Galante P.J., Soley-Guardia M., Boria R.A., Kass J.M., Uriarte M., Anderson R.P. (2014). ENMeval: An R package for conducting spatially independent evaluations and estimating optimal model complexity for Maxent ecological niche models. *Methods in Ecology and Evolution*. 5: 1198-1205.
