shapefile-simplify

Simplify shapefiles programmatically for mapbox Tileset/DataSource uploads using mapshaper.

Weighted Visvalingam simplification is used by default.

Prerequisites

The following dependencies are used for this project. Feel free to use other dependency versions as needed.

1. Windows 10 OS
2. NVM for Windows
   • v1.1.9
3. NodeJS
   • node version 10.16.3
   • npm v6.9.0
   • (installed via nvm)

Core Libraries and Frameworks

(See package.json for more information.)

1. mapshaper v0.5.28

Installation

1. Clone this repository.
   git clone https://github.com/ciatph/shapefile-simplify.git

2. Install dependencies.
   npm install

3. Create a .env file from the .env.example file. Update its defined variables in accordance with your personnal mapshaper cli command reference settings.

   Variable Name	Description
   PERCENTAGE	Percentage of removable points to retain on the shapefile.
   INPUT_FORMAT	input file format (i.e., .shp for shapefile, .geojson for GeoJSON)
   OUTPUT_FORMAT	file format of the simplified (i.e., shapefile for Shapefiles and geojson for GeoJSON)

   • The example .env file below will create a simplified GeoJSON file (small file size) from a (hi-resolution, big file size) shapefile:

     PERCENTAGE=1.5%
     INPUT_FORMAT=shp
     OUTPUT_FORMAT=geojson
     

   • The example .env file below will create a simplified shapefile from a (hi-resolution, big file size) shapefile:

     PERCENTAGE=4.0%
     INPUT_FORMAT=shp
     OUTPUT_FORMAT=shapefile
     

Usage

1. Create an INPUT directory named "shapefiles" inside the project's root directory. Put all shapefile-related input (.shp, .cpg, .dbf, .pfj and .shx) inside it.
2. Create an OUTPUT directory named "formatted" inside the project's root directory.
3. Run the npm script.
   npm start
4. Wait for the simplification process to finish. Simplified files will be generated in the /formatted directory.

@ciatph
20200120