21-conflict.rmd

---
title: "21. Conflict - Hadrian's Wall Tube Map"
output:
  rmarkdown::html_document:
    code_folding: hide
    theme: sandstone   
    highlight: tango
    css: "css/andrewl.css"
    includes:
      before_body: "partials/header.html"
      after_body: "partials/footer.html"
---
```{r setup, include=FALSE, message=FALSE, warning=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

> Want to see the code? Click on the black boxes on the right to show/hide the code. 

### Hadrian's Wall

Nothing says 'Conflict' like a the Roman Army. For nearly 300 years the Roman military from across the Empire
were stationed on Hadrian's Wall in the North of Englang. The wall is over 70 miles long and probably served 
a number of different purposes during that time.

So, along the wall were a number of forts and milecastles. The milecastles were small forts that were placed every
1200-1500 metres along the wall. They are about 20mx20m in size and usually guard a gate in the wall.

For this map I've taken the locations of the milecastles from the amazing Pleiades project
(https://pleiades.stoa.org/) and displayed them in a tube-map style. The horizontal spacing between the milecastles
is proportional to the distance between them, although I've kept them on a straight horizontal line.

The map is a little too large to see in detail on this page, but click on it to see the full image!

```{r map, include=FALSE, message=FALSE, warning=FALSE, results='hide'}

#First, we'll need to load a bunch of libraries so we can handle and view geospatial data
library(sf)
library(ggplot2)

#Next, we'll load the data we need from the Pleiades project
#This is a KML file that contains the locations of the milecastles
#produced by running an advanced search on the Pleiades website - https://pleiades.stoa.org/
milecastles <- st_read('./data/21/search.kml', quiet = TRUE)

# Convert to British National Grid, so we can work in metres
milecastles <- st_transform(milecastles, crs=27700)

# Tidy the data
# Remove any milecastles that are not actually milecastles (e.g. OSM boundaries)
milecastles <- milecastles[!grepl("OSM", milecastles$Name, ignore.case = TRUE), ]
milecastles <- milecastles[!grepl("boundary", milecastles$Name, ignore.case = TRUE), ]

# Add a column for the x position of the milecastles and a constant y position
milecastles$d <- st_coordinates(st_centroid(milecastles))[,1] 
milecastles$e <- 50

# Add a column for the milecastle name - we remove the "Milecastle (XX)" part of the name
milecastles$n <- gsub(".*\\((.*)\\).*", "\\1", milecastles$Name)
milecastles$n <- paste("   ", milecastles$n)

# Plot the milecastles - using imperial purple, of course
ggplot(milecastles, aes(x=d, y=e, label=n, background="white", color="purple")) +
geom_line(color="purple", size=3) +
geom_point(size = 3, shape = 21, color="black", fill = "transparent", stroke = 2) +
geom_point(color = "white", size = 2) +
geom_text(color="black", angle=90, hjust=0, vjust=0.5) +
theme_void() + 
theme(legend.position="none")

# Save the image
ggsave(file="images/milecastle-tube-map.png", width=28, height=5, dpi=360)
```

[![Alt text](images/milecastle-tube-map.png "Link title")](images/milecastle-tube-map.png)


### Credits

Data: [Pleiades](https://pleiades.stoa.org/) under CC-BY 3.0 license