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A
simple hierarchy is a continuum (from tallest to shortest, for example).
Complex hierarchies may require multiple methods of information arrangement
to adequately convey its information. The language
tree, for example, not only demonstrates the derivation of the
major languages, but also indicates when their parent language split
in relation to the development of other languages. A family tree is
also ordered by time (generations and birth order).
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 The
foundation of almost all good information architectures is a well-designed
hierarchy.
Louis Rosenfeld & Peter Morville, Information
Architecture for the World Wide Web |
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Hierarchies
can also be simple. Any qualitative comparison can be described with
a continuum. Cinema ratings systems, for example, allow movies to be
organised on the basis of reviewer response -- five stars great, 1 star
it sucks.
Information
can be organised from biggest to smallest, oldest to newest, largest
to smallest, graphics organisation based, for example, on predominant
colour. This site uses movement through the colour spectrum as a way
of indicating movement through various consecutive sections of the site.
Arranging items in a continuum indicates that this value scale is the
most important aspect of the data.
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One
of the most pervasive uses of hierarchy is the binomial system of
taxonomy. Taxonomy proceeds from the general to the specific.
Hierarchies, such as those described by taxonomy, typically produce
a 'tree-shaped' profile (albeit upside-down or lying horizontally)
which allow users to start at the general and then bore down to the
level of specific detail that suits them. It is this visual representation
of hierarchy that Mok means when he describes 'hierarchy' as one of
the seven methods to display information. The actual information displayed
in this format does not have to form a continuum -- e.g. many Tables
of Contents and indexes, whilst not strictly hierarchical, are set
out as 'trees'.
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By
definition, a hierarchical system of ideas begins with broad terms
and is subdivided into narrower terms. There is no perfect hierarchical
system of ideas, but your intended audience will bring to your system
some preconceived ideas on how information on their topic should
be organized. These people will have similar, but not exact preconceptions.
Biologist think similarly, just as computer scientists think similarly.
Morgan, Eric Lease 'Design
Elements for Great Web Pages: Readability, Browsability, Searchability
Plus Assistance' |
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Most site
indexes and ToC are based on tree-shaped hierarchies.
More
important information usually merits a more visible, higher-level position
in the hierarchy. So hierarchies are a useful way to guide your site's
users to what you believe they will find most important. A hierarchy
is not necessarily an index but an index is a hierarchy organised by
alphabet.
For
more about indexes >>
Most
Tables of Contents (ToCs) are based on hierarchies (whether they are
actually visually represented or not), with large topics differentiated
from each other, and then sub-topics indicated within each.
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A
genuine Contents list is not presented alphabetically, like the
many web pages mislabeled "Contents". A ToC or Outline is organized
by topical order, using a hierarchical tree structure. Every medium-length
page should appear in the site's Contents page. If a page is long
and contains many headings, then you can place a partial table
of contents (ToC) at the top of the page, and add '#' links to
automatically scroll down. ...Every web site, no matter how disorderly,
contains a hidden implicit structure. ...Any document structure
(collection of pages) that can be represented by box-and-arrow
diagrams can be represented helpfully and reasonably well by an
outline. ...The Table of Contents (ToC) is a structure-encapsulation
or structure-extraction device so powerful that it can present
an organized view that reveals the implicit structure of any web
site or document. ... Structured ToCs have a strong serendipity
factor. You can see adjacent, related topics, while an online
keyword search often hides that valuable structural information
from you.
...A
ToC doesn't necessarily have anything to do with a "good logical
reading order". A ToC is a structure of topics, not a sequence
of navigation. A good ToC doesn't imply some reading order, so
much as show a general logical relationship among all the topics.
Sequence of reading is only one item to consider when arranging
the topics in a logical structure. The important issue for automatic
ToC is, how good of a job has the author done at arranging a logical
tree of topics. The automatic ToC then portrays this tree structure,
for better or worse.
Michael Hoffman, 'Enabling
Extremely Rapid Navigation in Your Web or Document
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Images
show two methods of representing the same hierarchy.
Images
sourced from George Dillon, 'Making
Images of Structure', 1999
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In most
hierarchical systems each individual member will find itself on one
branch only. An animal, for example, cannot belong to two species. A
hierarchical index on a web site is seldom so circumscribed. Many pages
will be linked to from multiple other pages; 'Home' for example, will
usually be linked to from all pages except itself.
Strictly
enforcing hierarchical navigation structures can actually disable navigation
and REALLY annoy your users. In a 'pure' hierarchy, users would wear
themselves out running back and forth up one 'leg' of the hierarchy
and back and down another, to get to their desired content.
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A
taxonomy is an information organisation tool, constructed to enable
the user to gain an understanding of, and navigate around, available
information by means of a formal structure (arrangements) and labels
(names) to aid in locating it. A good taxonomy will take into account
the importance of separating elements of a group into subgroups
that are mutually exclusive, unambiguous, and taken together, include
all possibilities.
Agricultural Ontology Service Project Glossary |
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...hierarchy
is a familiar and powerful way of organizing information. In many
cases, it makes sense for a hierarchy to form the foundation for
organizing content in a web site. However, hierarchies can be fairly
limiting from a navigation perspective. If you have ever used the
ancient information browsing technology and precursor to the World
Wide Web known as Gopher, you will understand the limitations of
hierarchical navigation. In Gopherspace, you were forced to move
up and down the tree structures of content hierarchies (see Figure
4-3). It was not practical to encourage or even allow jumps across
branches (lateral navigation) or between multiple levels (vertical
navigation) of a hierarchy. The Web's hypertextual capabilities
removed these limitations, allowing tremendous freedom of navigation.
Hypertext supports both lateral and vertical navigation (see Figure
4-4). From any branch of the hierarchy, it is possible and often
desirable to allow users to laterally move into other branches.
For example, as you explore the Programs and Events section of a
conference web site, you may decide to register for that conference.
A hypertext link should allow you to jump to Registration without
first retracing your steps back up the Programs and Events hierarchy.
Louis Rosenfeld & Peter Morville, Designing
Navigation Systems |
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Nested
boxes are another way of visually indicating hierarchical organisation.
They are usually known as 'Treemaps'. Their ancestry may be traced to
Venn diagrams. They are designed to display a special class of trees
such as directory trees. Associated with each node in a directory tree
is a numeric value giving the size of the files contained in the subtree
rooted at the node. Each node is displayed as a rectangle proportional
to its value. All descendants of the node are displayed as rectangles
inside its rectangle. Treemaps allow for a simplified overview of the
information which the user can then drill down through to arrive at
the specific item of information that they want.
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Screen
from: HistoryWired:
A few of our favorite things
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Rosenfeld
and Morvilles' guidelines for designing information hierarchies
on the Web:
- Hierarchical
categories should be mutually exclusive. This isn't a hard-and-fast
rule, so feel free to put certain content in more than one
category. Don't overdo the cross-referencing, or your hierarchy
will get muddled.
- Consider
breadth and depth (the number of options at each level of
hierarchy and the number of levels in the hierarchy, respectively).
Don't make your users click through lots of levels to get
where they want (too much depth), and don't overwhelm them
with too many options on each page (too little depth). More
than 10 options on the main menu is overkill (too much breadth).
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Don't be dogmatic about the hierarchical model. If some of
your content lends itself to a database, don't put into a
hierarchy instead just because hierarchy is important.
Louis
Rosenfeld and Peter Morville, Information Architecture for
the World Wide Web
 See
also: Zaphiris, Panayiotis and Lianaeli Mtei Depth
vs Breadth in the Arrangement of Web Links = breadth more
effective than depth
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