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# Tutorial 3 -- Thematic map of world population
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## Overview
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This tutorial is designed to introduce a few more advanced Mapnik styling features, mainly `Rules` and `Filters`. This XML file is only compatible with Mapnik 2.x and above.
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This script should result in a graphic similar to:
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[[/images/world_population.png]]
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* Note: text labeling positions may be different between Mapnik versions.
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## Step 1: data
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For this tutorial we'll use the same world borders shapefile from natural earth used for the first two tutorials. Refer to either [Tutorial 1](GettingStartedInPython) or [Tutorial 2](GettingStartedInXML) for details.
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## Step 2: Script
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Save the below code into a file called `world_population.py`:
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```python
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#!/usr/bin/env python
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import mapnik
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mapfile = "world_population.xml"
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m = mapnik.Map(1400, 600)
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mapnik.load_map(m, mapfile)
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bbox = mapnik.Envelope(mapnik.Coord(-180.0, -75.0), mapnik.Coord(180.0, 90.0))
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m.zoom_to_box(bbox)
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mapnik.render_to_file(m, 'world_population.png', 'png')
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```
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## Step 3: Stylesheet
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Save the below XML into a file called `world_population.xml` in the same directory as the `world_population.py` python script:
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```xml
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<!DOCTYPE Map>
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<!-- Sample Mapnik XML template by Dane Springmeyer -->
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<Map srs="+proj=latlong +datum=WGS84" background-color="white" minimum-version="0.7.2">
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<Style name="population">
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<!-- Built from Seven Class sequential YIGnBu from www.colorbrewer.org -->
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<!-- Quantile breaks originally from QGIS layer classification -->
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<Rule>
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<Filter>[POP_EST] > -1 and [POP_EST] < 15000</Filter>
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<PolygonSymbolizer fill="#c7e9b4"/>
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<LineSymbolizer stroke="black" stroke-width=".1"/>
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</Rule>
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<Rule>
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<Filter>[POP_EST] >= 15000 and [POP_EST] < 255000</Filter>
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<PolygonSymbolizer fill="#7fcdbb"/>
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<LineSymbolizer stroke="black" stroke-width=".1"/>
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</Rule>
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<Rule>
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<Filter>[POP_EST] >= 255000 and [POP_EST] < 1300000</Filter>
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<PolygonSymbolizer fill="#1d91c0"/>
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</Rule>
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<Rule>
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<Filter>[POP_EST] >= 1300000 and [POP_EST] < 4320000</Filter>
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<PolygonSymbolizer fill="#41b6c3"/>
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</Rule>
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<Rule>
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<Filter>[POP_EST] >= 4320000 and [POP_EST] < 9450000</Filter>
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<PolygonSymbolizer fill="#225ea8"/>
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</Rule>
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<Rule>
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<Filter>[POP_EST] >= 9450000 and [POP_EST] < 25650000</Filter>
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<PolygonSymbolizer fill="#225ea8"/>
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</Rule>
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<Rule>
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<Filter>[POP_EST] >= 25650000 and [POP_EST] < 1134000000</Filter>
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<PolygonSymbolizer fill="#122F7F"/>
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</Rule>
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<Rule>
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<ElseFilter/>
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<!-- This will catch all other values - in this case just India and China -->
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<!-- A dark red polygon fill and black outline is used here to highlight these two countries -->
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<PolygonSymbolizer fill="darkred"/>
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<LineSymbolizer stroke="black" stroke-width=".7"/>
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</Rule>
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</Style>
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<Style name="countries_label">
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<Rule>
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<!-- Only label those countries with over 9 Million People -->
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<!-- Note: Halo and Fill are reversed to try to make them subtle -->
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<Filter>[POP_EST] >= 4320000 and [POP_EST] < 9450000</Filter>
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<TextSymbolizer size="7" fill="black" face-name="DejaVu Sans Bold" halo-fill="#DFDBE3" halo-radius="1" wrap-width="20">[NAME]</TextSymbolizer>
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</Rule>
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<Rule>
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<!-- Only label those countries with over 9 Million People -->
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<!-- Note: Halo and Fill are reversed to try to make them subtle -->
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<Filter>[POP_EST] >= 9450000 and [POP_EST] < 25650000</Filter>
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<TextSymbolizer size="9" fill="black" face-name="DejaVu Sans Book" halo-fill="#DFDBE3" halo-radius="1" wrap-width="20">[NAME]</TextSymbolizer>
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</Rule>
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<Rule>
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<!-- Those with over 25 Million get larger labels -->
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<Filter>[POP_EST] >= 25650000 and [POP_EST] < 1134000000</Filter>
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<TextSymbolizer size="12" fill="white" face-name="DejaVu Sans Book" halo-fill="#2E2F39" halo-radius="1" wrap-width="20">[NAME]</TextSymbolizer>
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</Rule>
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<Rule>
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<!-- Those with over 25 Million get larger labels -->
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<!-- Note: allow_overlap is true here to allow India/China to sneak through -->
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<Filter>[POP_EST] >= 1134000000</Filter>
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<TextSymbolizer size="15" fill="white" face-name="DejaVu Sans Book" halo-fill="black" halo-radius="1" wrap-width="20" allow-overlap="true" avoid-edges="true">[NAME]</TextSymbolizer>
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</Rule>
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</Style>
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<Layer name="countries" srs="+proj=latlong +datum=WGS84" status="on">
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<!-- Style order determines layering hierarchy -->
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<!-- Labels go on top so they are listed second -->
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<StyleName>population</StyleName>
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<StyleName>countries_label</StyleName>
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<Datasource>
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<Parameter name="type">shape</Parameter>
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<Parameter name="file">ne_110m_admin_0_countries.shp</Parameter>
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</Datasource>
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</Layer>
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</Map>
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``` |
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\ No newline at end of file |
