A high level overview of the concepts and tools required to produce maps using OpenStreetMap data using the Mapnik library.

1. Creating Maps from OpenStreetMap Data Using Mapnik Graham Jones 23 February 2011

3. Describe the structure of an osm2pgsql and a mapnik stylesheet.

4. Provide references to more detailed instructions.

6. It is not about detailed installation instructions for the tools – there are quite a few resources on the internet that do this.

7. References are provided at the end.

9. XAPI (if it is working)

11. Ideas about what information you would like to display, and how you would like to display it.

13. It is very powerful and can do all sorts – take data from different data sources, plot it in different ways depending on the map scale etc. With power comes complexity.

14. The main issue is that the usual way of using OSM data with mapnik is not to have mapnik read the data directly, but load the data into a database first, and mapnik gets the data from there. This means that you need a lot of tools to draw a map.

17. The OSM Mapnik Rendering Tools Key OSM Data file (.osm) PostgreSQL / postGIS database mapnik Mapnik stylesheet (.xml) Extra Data (Coastline Shapefiles etc.) generate_image.py or generate_tiles.py osm2pgsql default.style Files to be Edited / Customised Fixed data / programs / libraries

20. Reprojects the data from lat,lon values to mercator projection x,y positions.

21. Creates points, lines and polygons from the OSM nodes, ways and relations, to be compatible with mapnik.

23. It is a list of keys (highway, natural, waterway etc.). Only OSM entities with keys listed in default.style will be put into the database.

24. This means you need to think about which osm keys you will need to use to create your map before you import the database!

26. planet_osm_line : OSM linear ways.

28. A 'way' column which contains the geometry of the entity (e.g. position of a point).

31. e.g. SELECT way, name from planet_osm_point where historic is not null

32. The 'way' column is important – this tells mapnik where to plot the point!

34. <map>

35. <!ENTITY symboldir “/home/OSM/symbols/”>

36. <style>

37. define a style

38. </style>

39. <layer>

40. define a layer

41. </layer>

42. </map>

44. The initial <map> element defines things like the map projection to be used, and the background colour.

45. Layers define what data should be displayed .

46. Styles define how to display it .

48. But unless your style is extremely simple, there will be a lot of repetition – things like directory containing your map icons, your database username and password etc.

49. Entities are used to store this repeated data to make it easier to alter your stylesheet in the future.

52. <StyleName>Historic</StyleName>

53. <Datasource>

54. <Parameter name=&quot;type&quot;>postgis</Parameter>

55. <Parameter name=&quot;user&quot;>graham</Parameter>

56. <Parameter name=&quot;password&quot;>xxxx</Parameter>

57. <Parameter name=&quot;dbname&quot;>gis</Parameter>

58. <Parameter name=&quot;table&quot;>

59. (select way, name, historic from planet_osm_point where historic is not null) as points

60. </Parameter>

61. </Datasource>

62. </Layer> Style to use to display data Tell mapnik to use postgresql /postgis to get the data SQL Statement to extract data from the database

64. A style can have one or more rules that can define different ways of displaying the data (e.g. at different zoom levels).

65. <Style name=”Historic”>

66. <Rule>

67. <PointSymbolizer

68. file=&quot;&symbolDir;/tourist_ruin.n.16.png&quot;

69. />

70. </Rule>

71. </Style> This example style is as simple as it gets – just display an image, no matter what the zoom level. Reference to an Entity defined earlier in the file.

73. The only thing that needs altering in it is the bounding box that defines the are you want the map to cover.

74. generate_tiles.py is similar, but produces a set of tiles at various zoom levels for use on a web site.

76. There are more efficient tools for production services – try searching for mod_tile or tirex on the OSM wiki.

78. <!DOCTYPE Map[

79. <!ENTITY symbolDir &quot;/home/disk2/OSM/Maps/historic/symbols&quot;>

80. ]>

81. <Map

82. bgcolor=&quot;white&quot;

83. >

84. <Style name=&quot;Historic&quot;>

85. <!-- ************** Ruins / Abbeys *************** -->

86. <Rule>

87. <PointSymbolizer

88. file=&quot;&symbolDir;/tourist_ruin.n.16.png&quot;

89. allow_overlap=&quot;false&quot;

90. />

91. </Rule>

92. </Style>

93. <Layer name=&quot;Historic&quot; >

94. <StyleName>Historic</StyleName>

95. <Datasource>

96. <Parameter name=&quot;type&quot;>postgis</Parameter>

97. <Parameter name=&quot;user&quot;>graham</Parameter>

98. <Parameter name=&quot;password&quot;>1234</Parameter>

99. <Parameter name=&quot;dbname&quot;>gis</Parameter>

100. <Parameter name=&quot;table&quot;>

101. (select way from planet_osm_point where historic='ruins') as points

102. </Parameter>

103. </Datasource>

104. </Layer>

105. </Map>

106. And the result:

108. Test using the standard OSM style – get that working before you try to create your own style sheets.

109. Start with something very simple and build up from it.

111. A nice introduction to mapnik: http://www.slideshare.net/artemp/mapnik-sotm-2007

112. More information on mapnik: http://trac.mapnik.org/wiki/MapnikTutorials

113. What is this XML stuff?: http://en.wikipedia.org/wiki/XML

114. What is SQL?: http://www.w3schools.com/sql/default.asp