|
 
Diagrams
Diagrams (or graphics) are good for schematic representations, expressing ideas, or
futuristic objects. They are of course useful for displaying large amounts of data in the
form of charts. Where an image is of poor quality, and contains a certain amount of
detail, a graphic may be clearer. Graphical coding of objects can be effective. For
example different shaped elements can be used to represent components on an electrical
circuit, colours used to show political boundaries in an atlas, and line lengths and
angles to represent wind speed and direction on a map.
- Graphics can be used to accentuate or highlight essentials, for example to help in
identifying an object or feature.
- Graphics can be used to show objects that do not exist in reality, or can be used to
simplify a picture.
- Graphics are also necessary when information needs to be simplified. Thus a diagram or
map is more effective to show a route, rather than, say an aerial view of the roads to be
followed to reach a destination. Also the stylised map of the London Underground railway
is more effective for travellers than a more realistic diagram that shows all the actual
twists an turns in the railway lines.
- Graphical coding of objects can be effective; for example, different shaped elements can
be used to represent components of an electrical circuit, colours used to show political
boundaries in an atlas, and line lengths and angles to represent wind speed and direction
on a map.
- Careful design is needed to avoid inappropriate graphical coding and the overuse of
graphical codes. For example, the use of, colour, size and shape at the same time for
locations on a map, may overload the user, leading to degraded user performance or error.
Charts
The use of a chart or graph allows data to be interpreted conveniently to compare
values, show trends, and correlations. Some general notes on different types of chart are
shown below:
- Scatter chart
- This is a way of representing a two dimensional data sequence. In scatter charts data
points can be indicated by using graphical symbols. These symbols should be chosen to be
familiar to the users. A background grid to support the reading of exact values from a
chart may be used. Ideally the chart should be shown on a high resolution colour screen to
avoid interference of the grid with displayed data elements.
- Line Charts
- Shows how two continuous variables are related to each other, especially changes in one
variable over time. Time is normally shown on the horizontal. There should be a maximum of
4 lines per graph. If showing multiple lines, each should have an adjacent label and
possibly different symbols at data points with a different symbol per line. Line charts
should be displayed in high contrast to the background to enable good recognition of fine
lines. Background grids to support the reading of exact values from a chart should
preferably be used on high resolution colour graphic screens to avoid interference of the
grid with displayed data elements. Careful colouring is also needed.
- Bar charts
- Bar charts are suitable for data vectors with only one numerical value being shown for
different groups. They can be used to indicate the momentary status or last measured value
of a parameter in an analogue way to support quick and qualitative reading of important
variables. Quantity and development can be shown by means of bar charts. Scales can enable
more exact reading if necessary. Another application domain is in statistical analysis
(histograms etc.). Bar charts can also be used to show the breakdown of total figures by
splitting each bar up into segments e.g. how a budget is allocated to different spending
categories in a series of years.
- Pie charts
- Pie charts are suitable for showing the relationship or proportions of parts with regard
to a whole. They represent only a single row of data. By means of a pie chart important
parts of a whole can be emphasised by extracting relevant segments in the form of an
"exploding pie" chart.
- Simulated gauge
- A simulated gauge can be used to show a changing value in a familiar way. The benefit of
this technique is to show the value quickly in approximate terms against minimum and
maximum values. To allow the exact value to be read quickly, a combined digital and
analogue display may be used.
 Page 36 of 52 |
 Page 36 of 53 |
|
