lement attribute, such as link length, is stored in a vector). Compared to a "horizontal" structure, where a row in a table contains all the attributes of an element, a "vertical" one makes efficient use of the available computer memory space and also drastically reduces the number of disk accesses required to quickly and selectively access the EMME/2 data bank.
- Matrices: they are the standard means by which EMME/2 stores zone-related data:
- Matrices can be used to store input data (demand, socio-economic data, etc.) as well as results (travel time, travel distance, etc.);
- There are four types of matrices: full (O-D), origin, destination, and scalar;
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- A zone is identified by a centroid number; zones can be grouped into zone groups which are defined as sets within ensembles.
- Functions: they are data structures which contain algebraic expressions describing functional relationships. They are divided into six classes:
- an auto volume-delay function gives the travel time (in minutes) on a link of the auto network, as a function of link attributes;
- a turn penalty function gives the time for a turn (in minutes), as a function of turn attributes;
- a transit time function gives the travel time (in minutes) on a transit line segment, as a function of link, vehicle, line, and segment attributes;
- an auto demand function gives the auto demand (in persons), as a function of matrices and zone numbers;
- a transit demand function gives the transit demand (in persons/hour), as a function of matrices and zone numbers;
- a user-defined function is not linked to the data in the data bank. It permits the user to enter, manipulate and display functions of his choice by using general keywords.
C2) ArcInfo
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