Brendan Harmon

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Cartography in GRASS GIS

Landcover Map

Contents

Start GRASS

Download and extract the Governor’s Island Dataset for GRASS GIS. This geospatial dataset contains the GRASS GIS location nyspf_governors_island with raster and vector data for Governor’s Island, New York City, USA. Its coordinate reference system (CRS) is NAD_1983_StatePlane_New_York_Long_Island_FIPS_3104_Feet in US Survey Feet. Move the GRASS GIS location nyspf_governors_island to your GRASS GIS database directory. Start GRASS GIS, set the GRASS GIS database directory to GRASS GIS database directory, select nyspf_governors_island as your location, and open the PERMANENT mapset. Optionally download and install the free, open source font Lato.

Render Map Display

Layout a map of landcover with cartographic elements including a title and legend in GRASS GIS. First add the raster map landcover_2014 and resize your map display.

d.rast map=landcover_2014

Add cartographic elements to your map using either the toolbar at the top of the map display window or the command line. Add a title and descriptive text using the add text button in the add map elements menu or by running the module d.text from the command console. Optionally set the font, font color, and size. Position the text manually or using the at parameter in the command.

d.text -s text="Landcover" color=white at=2,98 font=Lato-Bold size=24
d.text -s text="Governor's Island" color=white at=2,95 font=Lato-Regular size=18
d.text -s text="New York City, USA" color=white at=2,92.5 font=Lato-Light size=18

Add a legend using the add legend button in the add map elements menu or by running the module d.legend from the command console. Set the raster to landcover_2014 and optionally set the font, font color, and size. Position and resize the legend manually or using the at parameter in the command.

d.legend -c raster=landcover_2014 at=70,89,2,5 color=white font=Lato-Regular fontsize=14

Add a scale bar and north arrow.

d.northarrow style=fancy_compass at=90.0,10.0 color=white text_color=white font=Lato-Regular
d.barscale at=72,5.8 length=500 units=feet segment=2 color=white bgcolor=none text_position=left fontsize=14

Render your map as a .png using the save display to file button in the map display window toolbar. This will save an image file from the map display at screen resolution.

Landcover Map
Landcover Map

To print a higher resolution map as an image or pdf use the addon module m.printws. This addon module uses the settings saved in a workspace file to print a map. First install the addon module with g.extension.

Save the workspace. In the File menu select Workspace and then Save as to save the workspace as landcover.gxw. Run m.printws Note that you may need to run m.printws --ui with the --ui flag to force the graphical user interface for the addon module to open. In m.printws set the workspace, the output file, the page type, and the format. Use the flexi page type to fit the landcover raster. Set the format to either png or pdf. After running the module, check the map it generated. The position of map elements may need to be adjusted. Reposition the map elements in the GRASS map display, save the workspace again, and re-run m.printws.

g.extension extension=m.printws
g.region raster=landcover_2014
d.rast map=landcover_2014
d.text -s text="Landcover" color=white at=2,95 font=Lato-Bold size=24
d.text -s text="Governor's Island" color=white at=2,92.5 font=Lato-Regular size=18
d.text -s text="New York City, USA" color=white at=2,90.5 font=Lato-Light size=18
d.legend -c raster=landcover_2014 at=70,89,2,5 color=white font=Lato-Regular fontsize=14
d.northarrow style=fancy_compass at=90.0,4.5 color=white text_color=white font=Lato-Regular
d.barscale at=72,5.8 length=500 units=feet segment=2 color=white bgcolor=none text_position=left fontsize=14
m.printws input=landcover.gxw output=landcover-150dpi.png page=Flexi format=png
150 DPI Landcover Map
Landcover Map at 150 DPI

Cartographic Composer

To render a high resolution map as a pdf use the cartographic composer g.gui.psmap. First set your computational region to the landcover raster.

g.region raster=landcover_2014

In the file menu select cartographic composer. A new window with the cartographic composer will open. In page setup set the units to mm, the page size format to custom, the width and height to 1000, and all margins to 0. Click on the map frame button and draw a frame over the entire canvas. In the map frame settings set fit frame to match current computational region. Set the resolution to at least 300 dpi. Uncheck draw border around the map frame. Click the add raster map layer button and set the raster to landcover_2014.

Add cartographic elements including a title, legend, and scale bar to the map. To add a title and text click on the add map elements button and select add text. In the text settings dialog, type Landcover as the text, set the font to Helvetica, the font size to 64, and the font color to white. In the position tab set the units to millimeters, the x position to 10, the y position to 20, and the reference point to the top left corner.

To add a legend click on the add map elements button and select add legend. In the raster legend settings check show raster legend and then set the source raster to current, the type of legend to discrete, set the units to millimeters, the x position to 10 and the y position to 50. Set the font to Helvetica, the font size to 36, and the color to white.

To add a scale bar click on the add map elements button and select add scale bar. In the scale bar settings set the units to millimeters, x position to 10, y position to 950, length to 1000 feet, height to 5 mm, segments to 2, font size to 36, and check transparent background.

Click the generate pdf output button to save the map.

Cartographic Composer
GRASS Cartographic Composer

Python

Maps can be automatically generated using the GRASS Python Scripting Library. This can be an efficient way to produce a large number of maps quickly. For a demo download the Python script render-map.py and run it in GRASS. In GRASS’ file menu choose launch script and browse to select render-map.py. The image landcover-2014.png will be written to your nyspf_govenors_island directory. See the tutorial Python in GRASS for a more detailed guide to using Python in GRASS.

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import os
import grass.script as gscript

# set environment
env = gscript.gisenv()
overwrite = True
env['GRASS_OVERWRITE'] = overwrite
env['GRASS_VERBOSE'] = False
env['GRASS_MESSAGE_FORMAT'] = 'standard'
gisdbase = env['GISDBASE']
location = env['LOCATION_NAME']
mapset = env['MAPSET']
res=1

# set region
gscript.run_command('g.region', raster='landcover_2014')

# write map to image file
gscript.run_command('d.mon',
    start="cairo",
    width=1600,
    height=1600,
    output=os.path.join(gisdbase, location, 'landcover-2014.png'),
    overwrite=overwrite)
gscript.run_command('d.rast',
    map='landcover_2014')
gscript.run_command('d.text',
    text='Landcover',
    font='Lato-Bold',
    size=24,
    color='white',
    at=(2,95),
    flags='s')
gscript.run_command('d.legend',
    raster='landcover_2014',
    font='Lato-Regular',
    fontsize=18,
    color='white',
    at=(70, 94, 2, 5),
    flags='c')
gscript.run_command('d.northarrow',
    style='fancy_compass',
    font='Lato-Regular',
    color='white',
    text_color='white',
    at=(92.5,5))
gscript.run_command('d.barscale',
    length='500',
    units='feet',
    segment=2,
    color='white',
    bgcolor='none',
    text_position='left',
    fontsize=18,
    at=(75,5.8))
gscript.run_command('d.mon', stop="cairo")
Landcover Map Rendered with Python
Landcover Map