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through K. c and c, are the alphabetic character restrictions.
Alphabetic character restrictions are constraints imposed over
individual and/or consecutive alphabetic characters in a
cartographic element. For example, two consecutive line
segments are perpendicular to each other.
In the general UMC expression (Formula 1), A and B are
alphabetic characters from the cartographic alphabet, or text, or
numerical expressions. U and U, are space dimensions
(coordinate values such as X, Y, and Z) and V and V, are image
construction operators.
4.4 A Model for Representing Spatial Data
The cartographic language provides an efficient mechanism to collect
and modify (consistently and systematically) individual features of a
spatial database or a map, but it is not enough to handle
simultaneously all of the information presented in a spatial database
or maps. This is accomplished by a cartographic model. A
cartographic model for the representation of spatial data is defined by
Ramirez and Lee (1991) as “a simplified representation of the surface
of the earth or any celestial body that can be expressed in analytical
form.” A cartographic model is only a generalization or idealization of
reality.
Major problems in the process of automating the collection of spatial
data are: (1) producers do not yet understand the nature of these
data or the mental process followed to collect them, (2) production is
operator-intensive and (3) computers are only used to accelerate
manual operations and simulate analog production methods. A
possible solution to this is to rethink the concept of mapping and
simplify the cartographic collection process to a well-defined set of
steps. This is the idea behind the cartographic model. Ideally, terrain
elements could be expressed by known functions of the type,
Element = F(Parameters), 2)
from which a cartographic product could be generated in a consistent
and efficient manner. Conceptually, the model will encompass all of
the rules employed by cartographic products today.
The cartographic form to be presented here was developed by
Ramirez and Lee (1991). It resembles the Bakus-Naur Form (BNF)
(1960) used in the definition of Algol; for this reason it is called the
Bakus-Naur Cartographic Form (BNCF). The BNCF is composed of
five basic symbols. This symbols are shown in Table No. 3.
Table No. 3
Dakus SINGU anges Form m
= : | € | Consists o C
<> Single occurrence of an abstraction
[1 Optional occurrence of an abstraction
{} Multiple occurrence of an abstraction
0 Always occurs together 0m
The context-free syntax of the language is given in the form of
production rules of the type, «A» :- «B» , where <A> is one of the
members of the production rule which is called the left-hand side
681
(LHS) of the production rule and «B» is the other member which is
called the right-hand side (RHS). They are always separated by the
symbol “=". The LHS is always of the type < > and it is a
nonterminal sign. Nonterminal signs are those abstractions which can
be expressed in terms of other terminal and nonterminal signs.
Terminal signs are known values, such as color, line weight, line
style, and coordinate values. The RHS could be of the type <>, [ ],
{}, (), any combination of them, and/or terminal signs. A derivation
is a set of production rules which enable the LHS to be fully
expressed by terminal signs.
Spatial data (topographic cartographic products) can be written in
terms of the BNCF. In order to do that, the cartographic components
of spatial data must be used. They are given in Table No. 4. Using the
above terminology, Ramirez and Lee (1991) found that any
topographic cartographic product can be expressed in BNCF by the
derivation given in Table No. 5.
Table No.1, the cartographic language (alphabet, operations,
rules, and writing mechanism), and the cartographic model
provide part of the conceptual framework needed for spatial data
collection and revision. Table No.l and the corresponding
discussion tell us how the terrain and its features change, the
cartographic rules tell us how features (new and old) behave, the
writing mechanism provides us with a systematic way to express
individual features, and the cartographic model allows
expression of the entire spatial database (or map) in a systematic
and formula-like fashion for collection or revision of spatial data.
Table No. 4
Cartographic Elements
| AP. area patterni
BS blank space
| CO color.
CUcurve
"EAlabel ——
LB line symbol
Une —
LN label number
LS linesign — —
LT line width Ta SS symbol size SE
LYlinestyle — _ ST structural grammar
NM name TS terminal sim
NN name number ——— VAvalue
OR orientation VVvisudlvariable —
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
