Choosing a Projection, Part 2: Pseudo-Conic, Azimuthal, and Cylindrical Projections

In the first part of this article, I argued against the use of Mercator and Equirectangular projections for web maps showing global data distributions and areas. Instead, an equal area projection is more appropriate because it preserves relative areas and data densities. In the final two parts, I shall look at some possible equal area ...

Choosing a Map Projection: Part 1

Previously in this series (1, 2), we discussed the different map projections and coordinate systems that can be used for map generation. We also looked at the reasons for the many different projections, and some of the reasons why we might wish to choose a different projection. In this article, I shall make the case ...

Map Projections and Coordinate Systems: Part 2

In the second part of this article, I shall look at map datums and coordinate systems. In the first half, published on Monday, I looked at different projection systems. As we saw in the first part, the map projection converts the curved surface of the Earth into a flat map. The datum is the model ...

Map Projections and Coordinate Systems: Part 1

This two part article is intended as an introduction to map projections and coordinate systems. The second part of the article will be published on Wednesday. They start a new series of articles which I shall be publishing over the next few weeks. I shall look at different projections and coordinate systems, the inadequacies of ...

The W3C Browser Geolocation API

The World Wide Web Consortium (W3C) have published a Geolocation API specification that allows a web page to query the user’s location using JavaScript to access objects exposed by the browser. Last Tuesday’s release of Firefox 3.5 was the first mainstream implementation of this API. This article demonstrates how to use the new geolocation functionality, ...

Animation and Dynamic Updates with KML

Although KML has quickly become the main format used for map annotation, it has a number of advanced features which only have limited support outside of Google Earth. Some of these absences are logical – for example, few mapping systems support 3d views and buildings. With the current pace of development it is likely that ...

WMS Tile Caches

The WMS standard is a popular choice for delivering map tiles from a web server. When combined with a modern AJAX client (eg. OpenLayers) it can produce a compelling geoweb application, but the download performance of WMS tiles can sometimes be inadequate. The easiest way to improve the WMS tile rendering performance for the end ...

Technical Overview: OpenLayers

OpenLayers is a popular open source JavaScript library for displaying dynamic map data in a web page. The OpenLayers library can work as the client half of an AJAX map application, including modern features such as “slippy” maps. Most if not all of the map data is provided by servers running other software. OpenLayers supports ...

Technical Overview: GeoRSS

GeoRSS is a standard for adding location information to an RSS feed. Example applications include travel blogs, news feeds, and real time earthquake feeds. Location information is typically a point location, but it can also include geographic lines, polygons, and related feature descriptions. Many online mapping services support GeoRSS, allowing map “mashups” to be easily ...

Technical Overview: GeoJSON

Although the acronym “AJAX” originally referred to Javascript and XML, the term has been generalized to cover any client language or data transfer format. A popular alternative to XML is JavaScript Object Notation (JSON). This is a much lighter format than XML, and is actually a subset of JavaScript. GeoJSON is a geospatial data interchange ...