local_mapshaper/README.md

In MazamaScience/MazamaSpatialUtils: Spatial Data Download and Utility Functions

Mapshaper

Mapshaper is a tool for editing spatial data, written in javascript. We mainly use it to simplify polygons. It has a web interface, found at mapshaper.org. It can also be downloaded locally, providing use of its command line interface. Full documentation can be found at github.com/mbloch/mapshaper.

Download

Mapshaper requires Nodejs. If you don't have it, follow the instructions at nodejs.org to install it.

With node, you can install the latest version using npm:

npm install -g mapshaper

That's all.

Mapshaper GUI

The mapshaper download comes with a GUI. You can run it with

mapshaper-gui

This will open a browser window, which you can add files to and perform actions like simplification.

You can also access the gui online at mapshaper.org.

Editing spatial data on the command line

Introduction to the command line tool

Full documentation for the command-line interface is available at: https://github.com/mbloch/mapshaper/wiki/Command-Reference

Mapshaper can be used on the following file formats: * Shapefile * GeoJSON * TopoJSON * DBF * delimited (CSV)

If your file is in some other format, you can use ogr2ogr (which comes with gdal) to convert it. Note that converting to a shapefile will automatically edit field names to be no longer than 10 characters.

Examples

# Read a Shapefile, simplify using Douglas-Peucker, output as GeoJSON
mapshaper provinces.shp -simplify dp 20% -o format=geojson out.json

WBDHUC

WBDHUC files are downloaded as .gdb from the USGS. They must be converted into something that can be read by mapshaper. The most efficient option is to convert them to Shapefiles. Note that converting to a shapefile will automatically edit field names to be no longer than 10 characters, and truncate values that are longer than 254 characters. Another option would be to convert to geojson. This will preserve the original data but will take much longer and generate much larger files, and can only be done one layer at a time.

Convert to shapefile

ogr2ogr WBD WBD.gdb -f "ESRI Shapefile"

Convert WBDHU2 to geojson

ogr2ogr WBDHU2.geojson WBD.gdb -f "GeoJSON" -skipfailures WBDHU2

Simplify to 2%

mapshaper WBDHUC2.shp -simplify 2% -o WBDHU2_02.shp

The Makefile in this directory has targets to download the WBD geodatabase file, unzip it, convert it to a shapefile, and simplify all the HUC layers in the shapefile to 1% and 2%. By default, all data is downloaded to ~/Data/Spatial but you can override this with SPATIAL_DATA_DIR.

Download and unzip geodatabase file to ~/Data

make SPATIAL_DATA_DIR=~/Data download_wbd

Convert geodatabase file to shapefile

You must already have WBD_National_GDB.gdb downloaded to SPATIAL_DATA_DIR

make SPATIAL_DATA_DIR=~/Data convert_to_shapefile

Simplify all HUC layers

make SPATIAL_DATA_DIR=~/Data simplify_all

Simplify only WBDHUC2

make SPATIAL_DATA_DIR=~/Data simplify_hu2

MazamaScience/MazamaSpatialUtils documentation built on Sept. 14, 2023, 6 p.m.