[OSM-newbies] The BIG mapping picture

Thomas Wood grand.edgemaster at gmail.com
Sat May 2 22:49:35 BST 2009


2009/5/2 Ernst Radema <Radema at xs4all.nl>:
> Hello all,
>
>
>
> Before I'll be able to answer my own question –as is obviously the intention
> of this newbies-list- I would like to ask for some information. Not on
> mapping details or (dis)functioning software features o rprograms, but on
> the BIG picture of the mapping process.
>
>
>
> In other words, what is the full process along which a map is created ?
>
>
>
>
>
> As far as my current knowledge goes the process must be something like this:
>
>
>
> ·         Recording of GPS-tracks as a collection of real word places.
>
> ·         Editing of GPS-tracks: conversion of points to map elements:
> roads, canals, POI, etc.
>
> o    Who decides and how is decided what all these points rare: eg in
> Holland ( where I live ) you often encounter a canal, a street, a bike path
> and a foot path next to each other.

Enter all the data you can collect, it's all useful! Usually the
people that do the map styles decide what gets rendered at different
scales etc.

> ·         Storage of all this information in a huge database (done in steps
> 1 and 2 )
>
> ·         Rendering of database information into visible map-images
>
> o    What are OSMarender ( sounds like OpenStreetMaps ) and
>
> o    Mapnik rendering ?

Osmarender and Mapnik are two different map renderers.
Osmarender maps are produced from osm files using XSLT to produce SVG
images that are then converted to PNG images.
Mapnik takes the data from a database and uses a C++ engine to render
directly to PNG or SVG as required.

> ·         Tiling: maps are cut into tiles of 0,25 x 0,25 degrees on a
> Tile-server.

Not quite, they're cut to whatever sizes are needed. We standardise on
256x256 pixels, with the data being in a spherical mercator
projection, meaning that the real world size represented changes based
upon latitude. (The full details are covered on wikipedia -
http://en.wikipedia.org/wiki/Mercator_projection)

> ·         Client request and presentation on a user interface
>
>
>
> Is this -more- or less- how mapping Works? Is it completely else? Who has
> more information, corrections, additions?

Roughly, the main aim of OSM is to collect the data, rather than the
rendering, we just do that because it's cool to be able to see what
you've done :)
Anyone is free to do (more or less) what they want with the data.

> All reactions welcome (except for the flaming J) !
>
>
>
> Ernst Radema
>
> Amsterdam, The Netherlands


-- 
Regards,
Thomas Wood
(Edgemaster)




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