## Description:

Taken from Cressie and Kapat (2008):

Between 1983 and 1989, a joint team from the British School in Athens, Greece, and the Universities of Amsterdam and Nottingham carried out an intensive survey of a 70 sq km area of Laconia across the Evrotas (ancient Eurotas) river, east from the ancient site of Sparta, Greece. These data consist of raw phosphate concentration readings (in mg P/100 g of soil) taken 10 m apart, from the site LS 165 of the Laconia Survey; the observations are distributed over a regular 16×16 grid (Buck et al. 1988). We denote these raw data by D(x, y), where (x, y) represents a location of a datum on the grid; x, y = 1, . . . , 16.

## Format:

A csv file containing a 16 x 16 matrix. The first row is at y = 16 and the final row at y = 1. The first column is at x = 1 and the last column at x = 16. Missing values are listed as -999.

## Usage:

To plot use the following

```
library(tidyr)
library(ggplot2)
X <- read.csv("~/Desktop/archaeology.csv",header = F)
names(X) <- 1:16
X <- gather(X,key = x,value=ph)
X <- mutate(X,y = rep(16:1,16))
X <- subset(X, !(ph < 0))
ggplot() + geom_tile(data=X,aes(x,y,fill=pmin(ph,150))) +
scale_fill_gradient(low="light yellow",high="red") +
coord_fixed()
```

## References:

Buck, C. E., Cavanagh, W. G., & Litton, C. D. (1988). The spatial analysis of site phosphate data. Computer and Quantitative Methods in Archaeology, 1, 151.

Cressie, N., & Kapat, P. (2008). Some diagnostics for Markov random fields. Journal of computational and graphical statistics, 17(3), 726-749.