[Case Study] Creating Map using Python

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1. import mapnik
   
2. 
   
3. LAYERS = [
   
4.     {'shapefile'  : "TM_WORLD_BORDERS-0.3.shp",
   
5.      'lineColor'  : "black",
   
6.      'lineWidth'  : 0.4,
   
7.      'fillColor'  : "#709070",
   
8.      'labelField' : "NAME",
   
9.      'labelSize'  : 12,
   
10.      'labelColor' : "black"
    
11.     }
    
12. ]
    
13. 
    
14. BACKGROUND_COLOR = "#a0c0ff"
    
15. 
    
16. BOUNDS_MIN_LAT  = 35.26
    
17. BOUNDS_MAX_LAT  = 71.39
    
18. BOUNDS_MIN_LONG = -10.90
    
19. BOUNDS_MAX_LONG = 41.13
    
20. 
    
21. MAX_WIDTH  = 1600
    
22. MAX_HEIGHT = 800

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关键词：Case study Creating python eating creat import

Second Step:Calculate Height and Width

1. extent = mapnik.Envelope(BOUNDS_MIN_LONG, BOUNDS_MIN_LAT,  BOUNDS_MAX_LONG, BOUNDS_MAX_LAT)
   
2. aspectRatio = extent.width() / extent.height()
   
3. 
   
4. mapWidth = MAX_WIDTH
   
5. mapHeight = int(mapWidth / aspectRatio)

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1. if mapHeight > MAX_HEIGHT:
   
2.     scaleFactor = float(MAX_HEIGHT) / float(mapHeight)
   
3.     mapWidth = int(mapWidth * scaleFactor)
   
4.     mapHeight = int(mapHeight * scaleFactor)

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1. map = mapnik.Map(mapWidth, mapHeight)
   
2. map.background = mapnik.Color(BACKGROUND_COLOR)

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1. or i,src in enumerate(LAYERS):
   
2.     style = mapnik.Style()
   
3.     rule = mapnik.Rule()
   
4. 
   
5.     if src['fillColor'] != None:
   
6.         symbol = mapnik.PolygonSymbolizer(
   
7.                     mapnik.Color(src['fillColor']))
   
8.         rule.symbols.append(symbol)
   
9.     if src['lineColor'] != None:
   
10.         symbol = mapnik.LineSymbolizer(
    
11.                     mapnik.Color(src['lineColor']),
    
12.                     src['lineWidth'])
    
13.         rule.symbols.append(symbol)
    
14.     if src['labelField'] != None:
    
15.         symbol = mapnik.TextSymbolizer(
    
16.                      mapnik.Expression(
    
17.                             "[" + src['labelField'] + "]"),
    
18.                             "DejaVu Sans Bold",
    
19.                             src['labelSize'],
    
20.                             mapnik.Color(src['labelColor']))
    
21.         symbol.allow_overlap = True
    
22.         rule.symbols.append(symbol)
    
23. 
    
24.     style.rules.append(rule)
    
25. 
    
26.     map.append_style("style-"+str(i+1), style)

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1. for i,src in enumerate(LAYERS):
   
2.     layer = mapnik.Layer("layer-"+str(i+1))
   
3.     layer.datasource = mapnik.Shapefile(file=src['shapefile'])
   
4.     layer.styles.append("style-"+str(i+1))
   
5.     map.layers.append(layer)

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1. map.zoom_to_box(extent)
   
2. mapnik.render_to_file(map, "map.png", "png")

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Reference

• Python Geospatial Analysis Cookbook
• Python Geospatial Development, 2nd Edition
• Learning R for Geospatial Analysis
• Learning Geospatial Analysis with Python, 2nd Edition
•