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include all 
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[TRIBUTES 
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WN names 
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cation, „use, 
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To each terrain feature in the database is assigned a 
unique feature code. The data model consisting of the 
map feature attributes and their relationships are 
derivable from the existing paper maps. 
Data points may not be duplicated on the same line 
segment, except in the case of closed features snapping to 
another, which will have its end-point coordinates 
duplicated on the intersecting line. Hydrographic 
features must snap to one another in order to allow for 
network analysis. Where such features have widths of 
five metres or more, they are considered to be bodies of 
water and are assembled into polygons. The perimeter of 
features and where practicable, isolated structures are 
recorded as closed polygons. Kerbs and edges of roads, 
tracks and running edges of railway tracks are connected 
as continuous strings (Akingbade, 2001). 
In all, there are two types of digital files produced, 
namely position files and cartographic files. The position 
files depict all features in their true geographic position 
and shape without regard to cartographic symbolisation 
and representation. The cartographic files are position 
files which had been enhanced by symbolisation for 
presentation at a particular scale. 
4. Digitalisation Initiative Bottlenecks 
There are several problems associated with the smooth 
running of the digitalisation initiative. These can be 
categorised into two, namely: those problems that are 
inherent in the 1:50,000 series in particular and general 
problems associated with mapping in Nigeria. 
4.1 Problems inherent in the 1:50,000 map series 
There are some limitations inherent in the 1:50,000 
topographic map series being digitised, which would not 
facilitate their conversion to digital format. Such limiting 
characteristics of the map series have been reported by 
Soneye (1999). Such problems include the following: 
4.1.1 Area (Polygon) feature depiction: On the 
1: 50,000 series, area features such as heavy forest, light 
forest, savannah/orchard bush, pack country, scrub, 
mangrove marsh, area liable to flooding and agricultural 
lands including palms are shown as point symbols in a 
manner that suggests that they are point features without 
due consideration for the possibility of determining their 
spatial extent (see figure 1). Figure 1 shows a section of 
the legend on the 1:50,000 series, depicting vegetation 
classes which are area features with point symbols. 
  
Heavy Forest... e e 
Light Forest ......… . , , À d 
+] Ü 
Savanna, Orchard Bush ERR 
#4, 
Cat 
Park Country. 0000000000 E 
Scrub... ais E RI 4 a ie 
Balms... La * i 
Mangrove . Aus À 
Marsh... creer slo das PUN - PN 
Areas Liable to Flood... | e 
Scattered Cuhivation. .. AP AA 
  
Plantation, ,....... = 
  
  
  
Figure 1: Vegetation classes depicted as point symbols 
Figure 2 shows the scattered manner in which these 
symbols are used on the map. 
  
      
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se eme entame iid 
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«Ki kinyinu 7 
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e 
  
  
  
  
Figure 2: Vegetation classes as depicted on map