Gmap4: REST and WMS Map Viewer for Google Maps and GIS Data

Gmap4 is a free for non-commercial use enhanced Google map viewer and GIS client (View KML, KMZ, GPX and TPO files, Google MyPlace files & delimited text files) by Joseph Elfelt. He thinks it's the first first general purpose REST and WMS viewer built on the Google Maps API.

This is a no-install solution for sharing online maps. The solution, for the end user, is just a URL that you put into a browser (see below). It points to the online service and then to the parameters of the map to display (layers, zoom level, etc.). Ideally, of course, the developer would put together that URL on the user's behalf and there are tools for non-programmers to create those URLs.

Elfelt describes Gmap4 this way:

It is easier to view GIS data with Gmap4 than almost any other viewer.  How easy?  “Click link - See GIS data”  That easy.

The following link starts Gmap4 and accesses two different WMS servers to display roads and an outline of the states.  A REST server is also accessed to display the USA weather radar.  When the map opens the GIS data is initially displayed on an ‘all white’ basemap.  To change the basemap and play with the layers, click the button in the upper right corner of the map.,-99.030762&z=5&t=Weather_radar,Transportation,States&wms= e=States&layers=states&transparent=true

Yes, someone that wants to make one of these Gmap4 links needs to learn how.  But once the link is made then anyone can click that link and see GIS data without having to know anything at all about GIS.  Plus, the user sees the familiar Google map interface and not a pile of spooky buttons they have never seen before.

I launched Gmap4 in 2009 as a general purpose file viewing tool.  It can display GPX, TPO, KML, KMZ, Google MyPlaces and delimited txt files.  Files can be hosted almost anywhere online.  It is popular with people that enjoy a wide range of outdoor activities in part because it displays high resolution topographic maps for the USA.  Simply zoom in somewhere and change the basemap (button in upper right corner) to “t4 Topo High”.  

The ability to also be a general purpose GIS viewing tool is a new feature.  Any data available via REST, WMS 1.3.0 and WMS 1.1.1 can now be displayed.  A Gmap4 link can display multiple layers from multiple WMS and/or REST servers.  After the map opens the user can turn layers on/off one at a time or all together.  The stacking order for transparent layers can also be changed.

If you open any Gmap4 link in the browser on a smartphone, tablet or other mobile device then an easy to use touch-friendly interface will be displayed.  Note that the browser has to be online.  Gmap4 does not have any offline ability.

All of the other Gmap4 features continue to work when GIS data is displayed. You can search, find your location, display a UTM grid, do trip planning, get a link that will display the map you see on your screen, etc.

All of the documentation for this GIS viewing feature, including plenty of examples, is written in plain language (not computer-speak!) and is at:

Gmap4 default map:

Gmap4 homepage:

I found the FAQ most helpful.

- via e-mail

Published Tuesday, August 6th, 2013

Written by Adena Schutzberg