Addressing multiple-scale output requirements
Gary S. Miller
Director - Project Implementation,Analytical Surveys, Inc.
741 N. Grand Avenue, Waukesha, WI 53186
M. Todd Rhodes
Project Implementation Analyst, Analytical Surveys, Inc.
741 N. Grand Avenue, Waukesha, WI 53186
Introduction
As geospatial information systems have spread throughout the enterprise, an increasingly diverse
user community has been born. These users have come to recognize the power of spatially
integrated information. Concurrent with an expansion of needs associated with user community
growth, the established user community has also increased its demands on geospatial systems.
Much emphasis has been placed on supporting these expanded needs with more open data
architecture, more standard computing platforms, friendlier user interfaces, and more robust
application functionality. These GIS enhancements have positively and substantially addressed
many system requirements.
The required ability of these systems to create a broadened range of optimized map displays and
products is a similarly important requirement. It is, however, a requirement that cannot be
addressed solely through software enhancement.
"The Map is only a Report"
Those of us who've been around the industry for a while have welcomed the expansion in users
and user demands. Many GIS professionals have also preached that the most important
components of the systems are the data and the applications. Statements like "the map is only a
report", and "don't worry about the map, it's the data that's important" have been heard by most
of us and spoken by some.
While those statements may be true, it's also true that a great deal of what GIS brings to the table
is its ability to present information in map-form. Map displays and outputs can be quickly
understood and communicated. The new user community has not simply been impressed by the
power of spatial computing, they have also been captivated by the power of spatial information
presentation.
The plane truth is that the ability to create clear, precise, appropriate, and aesthetically pleasing
map displays and products is among the most fundamental of the attributes which separate a GIS
from many other computing environments, but it does not come without some effort. In order to
further understand this effort, let's ask a few questions.
GIS has the ability to generate map displays and products. Why should we dedicate any
further thought to it?
Optimized map displays and products don't just happen. We design and develop GIS
databases and applications to supply them.
This sounds like much ado about nothing. GIS and CADD systems have had the ability to
create varying displays for years. Don't today's systems come with all the necessary
abilities to take care of this detail?
Yes they do, if we understand our requirements and properly use the technology.
What do we need to understand?
For starters, scale and size dependencies, map display, and product use.
Scale and Size Dependencies
Design of symbology and annotation sizing is a component of all GIS physical data modeling
efforts. A fundamental starting point in this process is considering the minimum readable size
and also the maximum reasonable size for a given scale. This consideration needs to be applied
to both symbology and annotation. Annotation sizing is somewhat easier to express, but the
readability and reasonability limits are essentially the same for both annotation and symbology.
Basically, assuming a "normal" reading environment, a minimum readable annotation (paper)
size may be approximately .06" (1.5mm). Also assuming a "normal" reading environment, a
maximum reasonable annotation size may be approximately .16" (4.0mm).
Within some GIS environments, annotation size is expressed in paper unit sizes as described
above, while in others it is specified in ground units. The table below presents the range of paper
sizes above, in ground units at several common scales.
Table 1: Annotation Size Ranges
As you can see in the table above, it's relatively easy to select an annotation size that is
appropriate for use at two scales where one scale is 2x, or even 2.5x the other. It is however,
essentially impossible to select an annotation size that is appropriate for two scales where one is
4x the other. For instance, 12' annotation falls within the readable and reasonable limits for both
1":100' and 1":200' scales. There is no size, however, that is both readable and reasonable at
1"100' and 1":400'.
Given, this assessment of annotation size ranges, it is possible to specify a single annotation size
for use at two scales, where one is double the other, but in cases where one scale is in excess of
2.5x the other, two separate annotation sizes will probably be required.
Guidelines for symbology sizing are essentially the same as those described above for annotation.
