6.3 REVISIÓN PRENSA ESCRITA DE LA CIUDAD DE PEREIRA

allowing them to learn and get com fortable with the functionality that was going to be tested. Also, any general questions about the dataset were discussed beforehand to assure participants understood, at least theoretically, the dataset they would encounter. The second phase included the actual testing, where users where given a set o f tasks or scenarios that they had to solve. Their interaction on-screen as well as any com m ents they made during the tasks were recorded using M atchware’s ScreenCorder (http://w w w .m atch w are.n et/). The third and final phase included a post-test interview to elicit participant views on the appropriateness o f the software tool for exploring spatial data visually. T he interview was taped for later analysis (see Table 3.4 for a summary o f all resources).

Tim e 1 hour 15 m inutes per test

Hardware 1 PC connected to the internet

D ictaphone

Software and data files Spotfire D ecisionSite and Map IS

ScreenCorder

Shapefiles (map and attribute data) E xcel file w ith data subset

Instructions D etecting relations, outliers and mistakes

C hoosing candidate locations

3.4

T h e T a s k s

An essential requirem ent o f usability tests is that the tasks are realistic. In other words, that they pose scenarios that potential users o f the system would need or w ant to address (Dumas and Redish 1999: 160). This implied a very careful design o f the tasks to be perform ed especially since the time available for testing was very limited. T he tasks were divided into two parts (Table 3.5). The first part was deliberately ill-defined so as to leave room for users to explore the dataset at will. Some guidelines or ‘inform ation to look for’ were provided only to limit the time users were to spend on the first part o f the test to about 20 minutes. H owever, there was no unique answer to the problem and the interest was m ore on analysing how participants interacted with the system and used the visualization tools to obtain inform ation from a spatial dataset that contained unknow n inform ation. Nevertheless, in terms o f accuracy, it was expected that users would be able to discover relations between variables as well as anomalies or potential mistakes in the dataset.

Usability' Evaluation in G eovisualization

Table 3.5 Tasks

Part 1

1. Find w hether variables in this dataset are related in som e way and w hether their relations occur in any particular areas o f Bristol.

2. Can you detect ‘outliers’ (unusual com binations o f attribute values)? 3. Can you d etect possible mistakes in the dataset entries?

Part 2

H aving explored the data, can you ch o o se candidate locations for (please take n ote o f the polygon ID):

4. A secondary sch ool

5. A gourm et shop______________________________________________________________________

The second part was aimed at testing w hether the software did provide an environm ent suitable for decision-making or problem solving with geospatial data. They implied identifying candidate locations that w ould be potentially suitable for an activity. Since visualization tools are not intended to be confirmatory but rather support a process o f hypotheses formation, there were no unique answers to the questions posed. O n the contrary, their outcom e was a function o f users’ criteria for addressing the task. F or instance for the task where they had to choose a location for a secondary school, they could choose the characteristics o f the catchm ent area (such as the households incom e level) where they would potentially have it built. The interest here was on observing how users would define a set o f criteria to make a decision with the data provided and w hether the system easily enabled this process. Table 3.6 summarises the two parts o f the evaluation and their aims.

Table 3.6 Tasks aims and description.

Concern T est Setup Task D escription C oncern T est Setup Task D escription Part 1

T esting w hether the present form in w hich Map IS and D ecisionSite are coupled helps users to acquire inform ation about or insight into a spatial dataset.

Users were asked to use all the d em oed visualizations.

Finding relations betw een variables and their location in space. D etectin g anomalies a n d /o r mistakes in the dataset.

Part 2

D etectin g w hether there w ere usability problem s w ith the interaction betw een Map IS and D ecision S ite for the purpose o f supporting spatial data exploration.

U sers were asked to ch o o se locations.

3.5

R e s u l t s

This section discusses some o f the usability problem s found with DecisionSite Map IS (for a detailed description see T obon 2002). In particular, features that facilitated or inhibited participant visual exploration o f the spatial dataset are m entioned as well as subject behaviour while using the tool. This is because, as Dix et al. (1998: 407) suggest:

addition to evaluating the system design in terms of its functional capabilities it is important to be able to measure the impact of the design on the user. This includes considering aspects such as how easy the system is to leam, its usability and the user’s attitude to it. In addition, it is important to identify areas of the design

which overload the user in some way, perhaps ly requiring an excessive amount of information to be remembered. ”

3.5.1

User Observations about the software

3.5.1.1 O b serv a tio n s o f S atisfaction

DecisionSite provides dynamic query devices (Chapter2) for perform ing structured queries on the fly (Ahlberg and Shneiderman 1994). Query devices can be im plem ented graphically in a num ber o f ways. Figure 3.2 shows their im plementation as two-way sliders that can be dragged by the user to reduce the num ber o f items in a view. An alternative is to use check boxes to select a num ber o f possible values, or radio buttons to select just one value o f an attribute. U nder the name o f alpha sliders (Ahlberg and Shneiderman 1994a), they have also been used to perform queries on text data. Users found the ability to dynamically filter data from the screen using the query devices and the possibility to plot the result onto a m ap to be the m ost innovative and salient functionality o f the environm ent. M ost o f them were not familiar with visualization packages but immediately recognized the value o f investigating spatial data interactively: ‘You can find [spatial] relationships directly using the m ap... This is really

cooir (User 7; see Table 3.2 for a reference to the users). T he query devices were perceived as

pow erful tools that enabled users to focus on subsets o f data and quickly find the inform ation they were interested in. They hide the structured query from the users very effectively, allowing them to concentrate on the exploration: ‘You do not need to build the query byyourself’ (\]se.T 8).

T he evaluation therefore highlighted the im portance o f enabling the user to focus upon subsets o f data. T he dynamic query filters serve this purpose. Providing similar functionality m ight be necessary n o t only when the dataset is large but also when the user needs to narrow dow n the data to those pertaining to a particular insight or hypothesis. Although a training period may be needed to m aster the use o f dynamic query filters, the devices have been

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significantly faster and m ore pleasant to use than other database query interfaces. It has also been argued that they are an easier m ethod to m aster for less expert users than SQL (Ahlberg gr a / 1992). AVE_FAM_SZ 0 H " '

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Figure ^2 Four different implementations o f Query D evices in DecisionSite (Boston, MA).

From left to right: Far Left) Range Sliders: users move the end o f the sliders or the slider itself to select a data range they want to appear in the graphical displays. B) Checkboxes: allow users to select more than one value o f an attribute to show in the graphical displays. C) Radio

Buttons: allow users to select only one value of an attribute. D) Alpha Sliders: allow the querying of text data.

Manipulating all elements o f a visualization (such as the colour coding o f objects on a scatterplot, their size and orientation) from a single properties window was also seen as an advantage, especially over doing the same operations using menus: “You don't have to go to look in menus to find rvhat you want to do which I think is really good because menus are only good when you

remember where things are” (User 3). Its use was rapidly learned and preferred to manipulating

each item o f a visualization separately. Users testified that this functionality was the m ost useful when substantial changes were needed. For instance in the PCP, the properties window was preferred when adding or deleting large numbers o f variables from the display.

Since the environm ent evaluated is windows based, m ore advanced users expect the system to comply with windows standards such as shortcuts. Furtherm ore, these users would expect some commands to be reserved for particular operations, i.e. control key plus m ovem ent o f the scroll wheel or button in the mouse to zoom in and out o f a view; or control key plus letter ‘s’ to save. Meeting these standards allows the user to recognise familiar functionality with ease and also to leam new contexts in which such functionality can be applied by analogy to systems that they already know. For instance, properties windows are increasin^y comm on in windows based systems. For this reason, they were seen as an advantage o f the system as it is a familiar feature with which to customise a view. Even when users did not expect or had not encountered this functionality before, properties windows were perceived

as a m ore efficient way for customising a view than manipulating it directly when many changes had to be made.

Advantages Frequency User Comments

Ease o f learning the system 8/9 “The graphics’ capabilities resemble S-Plus”; “Similar

things I ’ve seen before in D ata Desk ” (User 4); “Looks like E xcel’’ (User 2).

Ease o f using the system 8/9 ‘I t is really quick and very effective” (User 6).

Interaction betw een the GIS and D ecisionSite

7/9 “The ability to dynamically select points and to be able to see them on the map I think is very useful, because generally otherwise [ . . . ] you really have to juggle between

applications to do that” (User 7).