Bathymetry

Here are the steps I used for creating a bathymetric map in R. From where to download bathymetric data to how to read it and plot it in R.

Miriam Lerma true
2025-01-10

Intro

Bathymetry gives us information on the water depth around an area.

This post includes:
- Download raster data
- Read and subset raster data
- Plot raster data

Download raster data

GEBCO: General Bathymetry Chart of the Oceans provides information from bathymetry in the ocean.

To download visit webpage

Go to:
- Download data for user-defined areas
- Use the application
- Add your coordinates -here I use 1 to 10 and 50 to 60-
- Add to basket and download

Load

To download test data in tif format click here.

Select the directory where the information is stored, or as here, use the data directly form the repository.

Bath_tif<-'https://github.com/MiriamLL/TestData/raw/refs/heads/main/gebco_2024_n60.0_s50.0_w1.0_e9.0.tif'

Load the terra package for reading raster data

library(terra)

The function rast helps to read raster data - replacing package raster

Bath_file<-rast(Bath_tif)

Change to data frame

Bath_dataframe <- as.data.frame(Bath_file, xy = TRUE)

Alternatively, use the test information included in the package GermanNorthSea

##devtools::install_github("MiriamLL/GermanNorthSea")
library(GermanNorthSea)
Bath_dataframe<-GermanNorthSea::German_bath

Load the package tidyverse

library(tidyverse)

Use filter to subset your data

Bath_dataframe_sub <-Bath_dataframe  %>%
  filter(x > 2 & x < 10)%>%
  filter(y > 52 & y < 57)%>%
  rename(Bathymetry=3) %>%
  filter(Bathymetry < 10)

Plot

Load the package ggplot2

library(ggplot2)

Plot your data using geom_raster

ggplot() +
  geom_raster(data = Bath_dataframe_sub , aes(x = x, y = y, fill = Bathymetry)) +
  scale_fill_viridis_c(option = "mako")+
  theme_void()+
  theme(legend.position='bottom')+
  xlab('Longitude')+ylab('Latitude')+
  coord_sf(xlim = c(3,9), ylim = c(53,56),
                    label_axes = list(top = "E", left = "N", bottom = 'E', right='N'))

Load the package sf

library(sf)

Use the function st_transform to convert to the same CRS

German_land<-st_transform(GermanNorthSea::German_land, 4326)

Add the land to the plot using geom_sf

Plot_bath<-ggplot() +
  geom_raster(data = Bath_dataframe_sub , aes(x = x, y = y, fill = Bathymetry)) +
  geom_sf(data = German_land, colour = 'black', fill = '#ffffbe')+
  scale_fill_viridis_c(option = "mako")+
  theme_void()+
  theme(legend.position='bottom')+
  xlab('Longitude')+ylab('Latitude')+
  coord_sf(xlim = c(3,9), ylim = c(53,56),
                    label_axes = list(top = "E", left = "N", bottom = 'E', right='N'))
Plot_bath

More details about how to add features to a map here

Further reading