10 :: Map Projections

Really, I can think of no finer introduction to Map Projections other than comic above.

Here are some more boring details:

It is impossible to have all four aspects of a map be accurate (direction, distance, area, shape). In fact, you can’t get more than two. Mercator is good for direction and shape (Mapping with Drupal)

Ah, and here’s an explainer for the strange projection numbers I found in my earlier experiments in geolocation with OpenStreetMap

     .transform(
                         new OpenLayers.Projection("EPSG:4326"), //transform from WGS 1984
                             map.getProjectionObject() //to Spherical Mercator Projection
                                            );

Evidently, EPSG stands for European Petroleum Survey Group… which is now the International Association of Oil and Gas Producers.

And now I’m a little confused. The code above says that its using a Spherical Mercator Projection, but the documentation I’ve seen says that Spherical Mercator = EPSG:3857…

[researches].

Ah, found it. EPSG:4326 the projection that translates to latitude and longitude and is used by NATO and the GPS satellite navigation system.

Let’s end this post with a little map humour, shall we…

So, OpenLayers wants to use a single well-known number to describe the ‘Google Projection’ I talked about earlier. 54004/54005/41001 are all ‘well known’ as being a standard Mercator projection. Which is not the Google Projection.

So, in addition to http://spatialreference.org/ref/user/google-projection/ / http://spatialreference.org/ref/user/6/ , we need something we can use in “SRS” in WMS — an EPSG code, such as it was.

In order to pick one that doesn’t conflict.

It’s the ‘Google’ projection — so we picked 900913. (Google. In 1337-speak.)

l337!

Leave a Reply

Your email address will not be published. Required fields are marked *