MapShaper

MapShaper is a free online editor for Polygon and Polyline Shapefiles. It has a Flash interface that runs in an ordinary web browser. Mapshaper supports three line simplification algorithms: Douglas-Peucker, Visvalingam-Whyatt, and a custom algorithm designed to smooth convoluted coastlines and spiky features.

The MapShaper project was conceived in 2005 by Matthew Bloch and Mark Harrower at the University of Wisconsin, Madison Geography Department. A paper [pdf] from the 2006 AutoCarto conference describes how MapShaper works “under the hood.”

MapShaper is currently under development. This blog is intended to document the development process and let people test the latest version.

The latest online demo has expanded output options for map makers. MapShaper can now convert Polygon Shapefiles to Polyline Shapefiles and EPS files containing either lines or polygons. Converted Polyline Shapefiles contain an attribute field named “SHARED” that identifies those boundaries that are shared by two adjacent polygons. The polyline EPS output now uses a different color for shared and unshared boundaries.

MapShaper can now read PolygonM, PolygonZ, PolylineM and PolylineZ Shapefiles, but converts them to standard Polygon and Polyline Shapefiles (i.e. the data values are lost). With an eye to adding M and Z output, I would appreciate some feedback as to whether it would generally be good enough just to thin the M and Z data values as a Shapefile is simplified, or whether MapShaper should support averaging the values of retained vertices with the values of vertices that have been thinned out (assuming continuous range data).

Adobe just released a beta version of Flash Player 9 for Linux. This means that for the first time, Linux users will be able to use MapShaper.　You can download the new player here.

The latest update includes partial support for Polyline Shapefiles in addition to (clean) Polygon Shapefiles. I’m only claiming partial support because we’re not yet detecting intersections between polylines.

I’ll consider adding support for PolygonM, PolygonZ, PolylineM and PolylineZ Shapefiles if there is enough demand, so leave a comment or send email if you’d like to see support for other kinds of Shapefiles, or for other data formats than Shapefile.

– Matthew Bloch

MapShaper’s server now accepts uploads of up to 16 megabytes. Please let us know how MapShaper performs on larger Shapefiles!

The current demo (link at right) uses Actionscript 3. (Actionscript is the programming language for Flash interfaces). Porting MapShaper to Actionscript 3 sped up some of MapShaper’s functions by more than 10x. To show off the new, speedier MapShaper, I replaced the previous sample layer with a 6M Shapefile of countries of the world. Users can also upload and edit their own polygon Shapefiles.

– Matthew Bloch

Here are some of the features that we will be rolling out soon:

• Line smoothing
• Bezier curve fitting
• Brush selection / local editing