Map Projections

tutorial

grass

python

Map projections

Author

Brendan Harmon

Published

September 12, 2026

Modified

September 12, 2026

Setup

# Import libraries
import io
import sys
import subprocess
from pathlib import Path
import requests
from zipfile import ZipFile
import functools
import shutil

# Find GRASS Python packages
sys.path.append(
  subprocess.check_output(
    ["grass", "--config", "python_path"],
    text=True
    ).strip()
  )

# Import GRASS packages
import grass.jupyter as gj
import grass.script as gs
from grass.tools import Tools

Download land

Natural Earth

[2]

# Set url
url = "https://naciscdn.org/naturalearth/10m/physical/ne_10m_land.zip"

# Set path
data = Path.cwd() / "data"
data.mkdir(exist_ok=True)
land = data / Path(url).name

# Download dataset
request = requests.get(url, allow_redirects=True)
if request.status_code != 200:
    raise ConnectionError(f"Error downloading file: {request.status_code}")
land.write_bytes(request.content)
print(land)

# Unarchive dataset
with ZipFile(land, 'r') as archive:
    archive.extractall(path=land.parent)

# Delete archive
land.unlink()

Download graticules

Natural Earth

# Set url
url = "https://naciscdn.org/naturalearth/10m/physical/ne_10m_graticules_15.zip"

# Set path
data = Path.cwd() / "data"
data.mkdir(exist_ok=True)
graticules = data / Path(url).name

# Download dataset
request = requests.get(url, allow_redirects=True)
if request.status_code != 200:
    raise ConnectionError(f"Error downloading file: {request.status_code}")
graticules.write_bytes(request.content)
print(graticules)

# Unarchive dataset
with ZipFile(graticules, 'r') as archive:
    archive.extractall(path=graticules.parent)

# Delete archive
graticules.unlink()

Natural Earth II

[3]

# Start GRASS in Natural Earth II project
gs.create_project("natural_earth", epsg=54078, overwrite=True)
session = gj.init("natural_earth")
tools = Tools()

# Import natural earth vector
tools.v_import(input=land.with_suffix(".shp"), output="land")

# Print projection information
tools.g_proj(format="shell", flags="p").text

# Display projection
m = gj.Map(width=800)
m.d_vect(map="land", color="black", fill="black")
m.d_grid(size=15, color="black", flags="gbt")
m.show()

Equal Earth

[4]

# Create Equal Earth project
tools.g_proj(proj4="+proj=eqearth +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs +type=crs", project="equal_earth")

# Start GRASS in Equal Earth project
session = gj.init("equal_earth")
tools = Tools()

# Import natural earth vector
tools.v_import(input=land.with_suffix(".shp"), output="land") # epsg="4326", , flags="o"

# Print projection information
tools.g_proj(format="shell", flags="p").text

# Display projection
m = gj.Map(width=800)
m.d_vect(map="land", color="black", fill="black")
m.d_grid(size=15, color="black", flags="gbt")
m.show()

Airocean

[1]

# Create Airocean project
tools.g_proj(proj4="+proj=airocean +orient=horizontal +lon_0=0.0 +x_0=0.0 +y_0=0.0 +datum=WGS84 +type=crs", project="airocean") # vertical

# Start GRASS in Airocean project
session = gj.init("airocean")
tools = Tools()

# Import natural earth vector
tools.v_import(input=land.with_suffix(".shp"), output="land")

# Print projection information
tools.g_proj(format="shell", flags="p").text

# Display projection
m = gj.Map(width=800)
m.d_vect(map="land", color="black", fill="black")
m.show()

Peirce Quincuncial

# Create Peirce Quincuncial project
tools.g_proj(proj4="+proj=peirce_q +lon_0=25 +shape=square +datum=WGS84 +type=crs", project="peirce_quincuncial") # +shape=diamond

# Start GRASS in Peirce Quincuncial project
session = gj.init("peirce_quincuncial")
tools = Tools()

# Import land
tools.v_import(input=land.with_suffix(".shp"), output="land")

# Import graticules
tools.v_import(input=graticules.with_suffix(".shp"), output="graticules")

# Print projection information
tools.g_proj(format="shell", flags="p").text

# Display projection
m = gj.Map(width=800)
m.d_vect(map="land", color="black", fill="black")
m.d_vect(map="graticules", color="black", fill="none")
m.show()

van der Grinten IV

# Create van der Grinten IV project
tools.g_proj(proj4="+proj=vandg4 +datum=WGS84 +type=crs", project="vandg4")

# Start GRASS in van der Grinten IV project
session = gj.init("vandg4")
tools = Tools()

# Import land
tools.v_import(input=land.with_suffix(".shp"), output="land")

# Print projection information
tools.g_proj(format="shell", flags="p").text

# Display projection
m = gj.Map(width=800)
m.d_vect(map="land", color="black", fill="black")
m.show()

References

[1]

Robert W. Gray. 1995. Exact transformation equations for Fuller’s world map. Cartographica 32, 3 (1995), 17–25. https://doi.org/10.3138/1677-3273-Q862-1885

[2]

Nathaniel Vaughn Kelso and Tom Patterson. 2010. Introducing natural earth data. Geographia Technica 5, 1 (2010), 82–89.

[3]

Bojan Šavrič, Tom Patterson, and Bernhard Jenny. 2015. The Natural Earth II world map projection. International Journal of Cartography 1, 2 (2015), 123–133. https://doi.org/10.1080/23729333.2015.1093312

[4]

Bojan Šavrič, Tom Patterson, and Bernhard Jenny. 2019. The Equal Earth map projection. International Journal of Geographical Information Science 33, 3 (2019), 454–465. https://doi.org/10.1080/13658816.2018.1504949

Reuse

CC BY-SA 4.0

--- title: "Map Projections" author: Brendan Harmon date: 2026-09-12 date-modified: today license: CC BY-SA categories: [tutorial, grass, python] description: > Map projections image: images/projections-03.webp bibliography: grass.bib links: g_region: "[g.region](https://grass.osgeo.org/grass-stable/manuals/g.region.html)" format: ipynb: default html: toc: true code-tools: true code-copy: true engine: jupyter execute: eval: false jupyter: python3 --- ![Airocean](images/projections-03.webp) ## Setup ```{python} # Import libraries import io import sys import subprocess from pathlib import Path import requests from zipfile import ZipFile import functools import shutil # Find GRASS Python packages sys.path.append( subprocess.check_output( ["grass", "--config", "python_path"], text=True ).strip() ) # Import GRASS packages import grass.jupyter as gj import grass.script as gs from grass.tools import Tools ``` ## Download land [Natural Earth](https://www.naturalearthdata.com/) [@Kelso:2010] ```{python} # Set url url = "https://naciscdn.org/naturalearth/10m/physical/ne_10m_land.zip" # Set path data = Path.cwd() / "data" data.mkdir(exist_ok=True) land = data / Path(url).name # Download dataset request = requests.get(url, allow_redirects=True) if request.status_code != 200: raise ConnectionError(f"Error downloading file: {request.status_code}") land.write_bytes(request.content) print(land) # Unarchive dataset with ZipFile(land, 'r') as archive: archive.extractall(path=land.parent) # Delete archive land.unlink() ``` ## Download graticules [Natural Earth](https://www.naturalearthdata.com/) ```{python} # Set url url = "https://naciscdn.org/naturalearth/10m/physical/ne_10m_graticules_15.zip" # Set path data = Path.cwd() / "data" data.mkdir(exist_ok=True) graticules = data / Path(url).name # Download dataset request = requests.get(url, allow_redirects=True) if request.status_code != 200: raise ConnectionError(f"Error downloading file: {request.status_code}") graticules.write_bytes(request.content) print(graticules) # Unarchive dataset with ZipFile(graticules, 'r') as archive: archive.extractall(path=graticules.parent) # Delete archive graticules.unlink() ``` ## Natural Earth II [ Natural Earth II](https://proj.org/en/stable/operations/projections/natearth2.html) [@Šavrič:2015] ```{python} # Start GRASS in Natural Earth II project gs.create_project("natural_earth", epsg=54078, overwrite=True) session = gj.init("natural_earth") tools = Tools() # Import natural earth vector tools.v_import(input=land.with_suffix(".shp"), output="land") # Print projection information tools.g_proj(format="shell", flags="p").text ``` ```{python} # Display projection m = gj.Map(width=800) m.d_vect(map="land", color="black", fill="black") m.d_grid(size=15, color="black", flags="gbt") m.show() ``` ![Natural Earth II](images/projections-01.webp) ## Equal Earth [Equal Earth](https://proj.org/en/stable/operations/projections/eqearth.html) [@Šavrič:2019] ```{python} # Create Equal Earth project tools.g_proj(proj4="+proj=eqearth +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs +type=crs", project="equal_earth") ``` ```{python} # Start GRASS in Equal Earth project session = gj.init("equal_earth") tools = Tools() # Import natural earth vector tools.v_import(input=land.with_suffix(".shp"), output="land") # epsg="4326", , flags="o" # Print projection information tools.g_proj(format="shell", flags="p").text ``` ```{python} # Display projection m = gj.Map(width=800) m.d_vect(map="land", color="black", fill="black") m.d_grid(size=15, color="black", flags="gbt") m.show() ``` ![Equal Earth](images/projections-02.webp) ## Airocean [Airocean](https://proj.org/en/stable/operations/projections/airocean.html) [@Gray:1995] ```{python} # Create Airocean project tools.g_proj(proj4="+proj=airocean +orient=horizontal +lon_0=0.0 +x_0=0.0 +y_0=0.0 +datum=WGS84 +type=crs", project="airocean") # vertical ``` ```{python} # Start GRASS in Airocean project session = gj.init("airocean") tools = Tools() # Import natural earth vector tools.v_import(input=land.with_suffix(".shp"), output="land") # Print projection information tools.g_proj(format="shell", flags="p").text ``` ```{python} # Display projection m = gj.Map(width=800) m.d_vect(map="land", color="black", fill="black") m.show() ``` ![Airocean](images/projections-03.webp) ## Peirce Quincuncial [Peirce Quincuncial](https://proj.org/en/stable/operations/projections/peirce_q.html) ```{python} # Create Peirce Quincuncial project tools.g_proj(proj4="+proj=peirce_q +lon_0=25 +shape=square +datum=WGS84 +type=crs", project="peirce_quincuncial") # +shape=diamond ``` ```{python} # Start GRASS in Peirce Quincuncial project session = gj.init("peirce_quincuncial") tools = Tools() # Import land tools.v_import(input=land.with_suffix(".shp"), output="land") # Import graticules tools.v_import(input=graticules.with_suffix(".shp"), output="graticules") # Print projection information tools.g_proj(format="shell", flags="p").text ``` ```{python} # Display projection m = gj.Map(width=800) m.d_vect(map="land", color="black", fill="black") m.d_vect(map="graticules", color="black", fill="none") m.show() ``` ![Peirce Quincuncial](images/projections-04.webp) ## van der Grinten IV [van der Grinten IV](https://proj.org/en/stable/operations/projections/vandg4.html) ```{python} # Create van der Grinten IV project tools.g_proj(proj4="+proj=vandg4 +datum=WGS84 +type=crs", project="vandg4") ``` ```{python} # Start GRASS in van der Grinten IV project session = gj.init("vandg4") tools = Tools() # Import land tools.v_import(input=land.with_suffix(".shp"), output="land") # Print projection information tools.g_proj(format="shell", flags="p").text ``` ```{python} # Display projection m = gj.Map(width=800) m.d_vect(map="land", color="black", fill="black") m.show() ``` ![van der Grinten IV](images/projections-05.webp)