Distance to coast

In this blog post, I share a step-by-step guide on how to use raster data from distance to the coast. I walk you through the steps I used using the North German Sea as an example.

Miriam Lerma true
2025-02-20

Intro

Distance to coast gives us information on the distance (in meters) from one point at sea to the nearest coast.

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

Distance to coast

To download:
- Access OceanColor NASA
- Select the interpolated 0.01-degree GeoTiff packed together with a brief description file.
- Unzip information.

Read and subset

To read from file.

Select the directory where the information is.

library(here)
here()
this_folder<-paste0(here(),"/_posts/2025-02-15-distancetocoast")
this_file<-paste0(this_folder,"/GMT_intermediate_coast_distance_01d.tif")

Use the package terra to use the function rast.
Then convert to data frame.

library(terra)
DistCoast_file<-rast(this_file)
DistCoast_dataframe <- as.data.frame(DistCoast_file, xy = TRUE)
beepr::beep(sound=1)

The file is quite large, so I recommend to subset the data to the area of interest.

Here I select the area close to the German North Sea.

library(tidyverse)
DistCoast_dataframe_sub <-DistCoast_dataframe  %>%
  filter(x > 2 & x < 10)%>%
  filter(y > 52 & y < 57)%>%
  rename(Dist=3) %>%
  mutate(Dist = as.numeric(Dist))
beepr::beep(sound=1)

To save as rda would make the reading a lot faster.

German_distancecoast<-DistCoast_dataframe_sub
save(German_distancecoast, file="German_distancecoast.rda")

Alternatively, access the information from the package GermanNorthSea.

library(GermanNorthSea)
DistCoast_dataframe<-GermanNorthSea::German_distancecoast

Plot

To plot adding land.

library(sf)

Make sure is in the same CRS.

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

To exclude information on land.

library(tidyverse)
DistCoast_dataframe_sub<-DistCoast_dataframe %>%
  filter(Dist > -20)

Use ggplot to create your plot.

Plot_distance<-ggplot() +
  geom_raster(data = DistCoast_dataframe_sub, aes(x = x, y = y, fill = Dist)) +
  geom_sf(data = German_land, colour = 'black', fill = '#ffffbe')+
  scale_fill_viridis_c(option = "rocket")+
  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_distance+
  guides(fill=guide_legend(title="Distance to coast"))

Further reading