Addressing multiple-scale output requirements
The Software Takes care of IT
Each of the leading GIS software products feature various mechanisms that address some of the
issues described above. None, however, fully address the issues above in a purely automated
manner.
For instance, the automated or semi-automated re-sizing of symbology and annotation is
supported by nearly every system. Symbology positioning and annotation positioning and
frequency modification, however, is not perfectly supported by any system. Similarly, every GIS
software system allows for adjustment of content and emphasis for various displays and products,
but no implementation of the software will achieve optimum results without first defining what
the optimized results are.
The simple truth is that the relevant mechanisms within the software environments act as both
tools and constraints that must be considered in the design of the physical data model.
Analysis of "Multi-Scale" Requirements
The only way to assure that multiple scale requirements are met by a geospatial system
implementation is to include certain relevant issues within the requirements analysis and logical
data model design prior to initiating the physical database design process.
The first step in this process is the consideration of the support of map displays and products as
system requirements in the same way that the support of applications and interfaces are
considered as system requirements. This means that just as individual applications and interfaces
must be identified as part of a requirements analysis effort, important map displays and products
must be individually identified.
As with applications and interfaces, the examination of needs of the relevant user group must be
accomplished first. As stated earlier, the relevant questions are who, why, how, when, and under
what conditions will the map display or product be used.
Once these questions have been answered, a list of map displays and products can be developed.
For each of map display and product, a scale and size must then be determined. Following that
effort, the content of the map display and product must be considered. This process is most
effectively done at a feature-by-feature, component-by-component level.
The use of a matrix where, features and components form the left column and map displays and
products (with scale and size noted) form the top row. The intersecting cells of the matrix can
then be used to note whether a particular feature component is required for each map display or
product. In the case of symbols, initially noting simply whether it is required as a YES or NO
may be sufficient. For annotation, however, it may be necessary to note the specific content
requirement for each annotation string. For linear features, it may also be necessary to note the
required or desired frequency of the annotation. A sample matrix is presented below as table 2.
Table 2: Component Display Requirement Matrix
The resultant matrix concisely presents the display requirements of each map product. The
guidelines for symbology and annotation readability and reasonability, can then be applied to
determine what specifications are appropriate for each feature component on each product. Some
compromise of optimal specifications for each display or product may be appropriate at this time.
Once this process is completed, a practical test of the displays and products is the next logical
step. This can typically be accomplished within a CADD environment without benefit of full
GIS functionality. The process for accomplishing this is to digitize a typical map area
graphically differentiating between components to the same degree that the GIS would
differentiate between components.
"Normal" CADD functionality can then be used to simulate the map displays and products
required by the GIS. This process might involve changing display and plot scale, copying and resizing
symbology and annotation, and editing certain annotation. Care must be taken to
accomplish this effort without inadvertent symbol or annotation repositioning.
The resultant displays and products can then be examined to determine to what extent they meet
user requirements. This examination may point to requirements that were overlooked in the
initial analysis or specifications that are unsuitable. In these situations, some modification to the
display and product requirement matrix, and the sample displays and products may be merited
Once the matrix and the samples have been edited, they will be extremely helpful in the physical
data modeling effort and in the further development of specifications.
Conclusion
The ability to create optimized map displays and outputs is a critical requirement for an
enterprise-wide geospatial system. This requirement may be more complex than it appears at
first glance. The GIS software available today provides the basic ability to support multiple
displays and products. Particularly, when it comes to varying scales, the best use of those
abilities requires a detailed analysis of the relevant requirements. In order to avoid substantial
additional cost and effort, this analysis must be accomplished prior to the physical database
design, development, and construction.
