Ridgelines – r.iresmi.net

Author

Michaël

Published

2025-11-02

Modified

2025-11-02

A photo of a hiking trail below a steep ridge in the clouds — Hiking Path – CC BY-NC-SA by HD

Day 2 of 30DayMapChallenge: « Lines » (previously).

Representing a digital elevation model as ridgelines…

Config

library(elevatr)
library(rnaturalearth)
# remotes::install_github("ropensci/rnaturalearthhires")
library(terra)
library(ggplot2)
library(ggridges)

Data

ch <- ne_countries(scale = 10, country = "switzerland")

ele <- get_elev_raster(ch, z = 9)
names(ele) <- "z"

Map

ele |> 
  mask(ch) |> 
  aggregate(fact = 20) |> 
  as.data.frame(xy = TRUE) |> 
  ggplot() +
  geom_density_ridges(aes(x = x, y = y, group = y, height = z),
                      stat = "identity",
                      alpha = 0.3,
                      color = "red",
                      fill = "white",
                      scale = 10) +
  labs(title = "Switzerland",
       caption = paste("Elevation data from
       https://registry.opendata.aws/terrain-tiles
                      https://r.iresmi.net/", Sys.Date())) +
  theme_void() + 
  theme(plot.background = element_rect(fill = "grey"),
        title = element_text(color = "red"),
        plot.caption = element_text(color = "#777"),
        plot.margin = margin(2, 2, 2, 5, unit = "mm"))

A map of Switzerland altitude — Figure 1: Swiss ridgelines

---
title: "Ridgelines"
description: "Day 2 of 30DayMapChallenge. Lines"
author: "Michaël"
date: "2025-11-02T00:00:00"
date-modified: last-modified
categories:
  - R
  - raster
  - datavisualization
  - 30DayMapChallenge
draft: false
freeze: true
editor_options:
  chunk_output_type: console
chunk_output_type: console
execute:
  eval: true
---

[![Hiking Path – CC BY-NC-SA by HD](images/53210381276_a267ec666d_c.jpg){.preview-image alt="A photo of a hiking trail below a steep ridge in the clouds"}](https://www.flickr.com/photos/hdz/53210381276/)

Day 2 of [30DayMapChallenge](https://30daymapchallenge.com/): « Lines » ([previously](/#category=30DayMapChallenge)).

Representing a digital elevation model as ridgelines...

## Config

```{r}
#| label: setup

library(elevatr)
library(rnaturalearth)
# remotes::install_github("ropensci/rnaturalearthhires")
library(terra)
library(ggplot2)
library(ggridges)
```

## Data

```{r}
#| label: data

ch <- ne_countries(scale = 10, country = "switzerland")

ele <- get_elev_raster(ch, z = 9)
names(ele) <- "z"
```

## Map

```{r}
#| label: fig-map
#| fig-cap: Swiss ridgelines
#| fig-alt: A map of Switzerland altitude
#| out-width: 100%
#| fig-width: 7
#| crop: true

ele |> 
  mask(ch) |> 
  aggregate(fact = 20) |> 
  as.data.frame(xy = TRUE) |> 
  ggplot() +
  geom_density_ridges(aes(x = x, y = y, group = y, height = z),
                      stat = "identity",
                      alpha = 0.3,
                      color = "red",
                      fill = "white",
                      scale = 10) +
  labs(title = "Switzerland",
       caption = paste("Elevation data from
       https://registry.opendata.aws/terrain-tiles
                      https://r.iresmi.net/", Sys.Date())) +
  theme_void() + 
  theme(plot.background = element_rect(fill = "grey"),
        title = element_text(color = "red"),
        plot.caption = element_text(color = "#777"),
        plot.margin = margin(2, 2, 2, 5, unit = "mm"))
```