Database Development for Chennai City
The road network of Chennai City
is digitised using PC ArcInfo. The source of the map is survey of land record
map. This map is drawn based on Survey of India map and its scale is 1:33,000.
The road network of Chennai City is digitised by considering all the roads in
the map. Total of nine spatial locations were identified as control points to
project the map in to its real world co-ordinates. The concept of geographic
database, is to structure the data according to certain number of logical rules.
The geographic database of Chennai City is conceived and elaborated under the
GIS Arc/Info Software. The Structure of database is shown in the figure below.
The minimum road
width for the development of database is taken as 12m width. The reason of
choosing 12m width is, as per detailed development plan, only roads with more
than 12m width is considered as Public Roads. Hence three levels of road network
is taken as follows:
- I Order Roads - road width of more than 24 m
- II Order Roads - road width of between 18 m – 24 m
- III Order Roads - road width of between 12 m – 18 m.
Database is developed for all the above road network level. The database is
developed for road length of 7. 35 km in I Order roads, 16.79 km in II Order
roads and 85.08 km in III Order roads. The data in the database are also
categorized as Group 1 and Group 2. The purpose of this classification is that
only Group 1 data is used for further analysis in this work. For all the above
development, Simple Macro Language(SML) have written for graphical user
interface(GUI) .Road network level and its database for Chennai City are shown
in the form of maps as below. Identification of Critical
After developing the road network database for Chennai City,
Chepauk area is taken as study area for the analysis. The Chepauk comes under
the planning division of 11, unit no.2 in Detailed Development plan prepared by
Chennai Metropolitan Development Authority. The approximate extent of the land
is 47 hectare. A map showing the database of the study area is shown below.
The critical link
among the selected stretch is identified based on model generated by Analytic
hierarchy process (AHP) technique. The composite index is found by using the
model and AHP technique is used to generate scores for the factors that are
considered for analysis. The composite index for various are generated by the
model and the lowest model value indicates the critical link of the selected
study area. Also, the positive and negative impact of the factors towards the
objective of the work is taken in to account in deriving the model value.
Critical links are identified by considering the following factors.
Model Development and its
- Carriage way width
- Footpath width
- Volume on the road
- Capacity of road
- Average Speed
- Percentage of Slow Moving Vehicles.
For the present study, the spatial- AHP technique
(integrating the GIS database in the AHP frame work) is applied to find the
relative importance weight (RIW) for each decision factor. The composite index
for each road is determined by aggregating the relative importance weights at
each level of the hierarchy. The RIWs are normlsed eigenvectors corresponding to
the maximum eigenvalues of the pairwise comparison matrices constructed at each
level of the decision hierachy. The RIW assigned to each hierarchy element is
deremined by normalising the eigenvector of decision matrix.
are eatimated by multiplaying all the elements in a row and taking the root of
the product, where in is the number of row elements. Normailsation of the eigen
vector is accomplished by dividing each eigen vector element by the sum of the
eigen vector elements of the decision matrix. After finding the relative
importance of various factors, a model is developed for finding a composite
index for various roads which assists in identifying the critical links.
The scores for each factor on scale of 9 are as follows :
|Percentage of SMV
above model is then developed and fed in the PC ArcInfo. The Model equation is
5.5Ri1 + 1.89Ri2 + 1.57Ri3 + 0.68Ri4 + 0.35 Ri5 (
Ri1-5 - standard value for jth parameter for route
i - S elected rotes from 1 to n
The index value for various
stretches is obtained by above formula. The values are stored in “TABLES” and
the positive and negative impact of decision factors is taken in to account.
Then the critical links is identified based on the index value in such a way
that lower the index value the link is more critical.