DOT/FAA/AM-00/8

U.S. Department

of Transpor tation

Federal Aviation

Administration

Kevin W. Williams

FAA Civil Aeromedical Institute

Oklahoma City, OK 73125

February 2000

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

Office of Aviation Medicine

Washington, DC 20591

Comparing Text and

Graphics in Navigation

Display Design
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents thereof.
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AM-00/8

4. Title and Subtitle 5. Report Date

Comparing Text and Graphics in Navigation Display Design February 2000

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

Williams, K.W.

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aeromedical Institute

P.O. Box 25082

Oklahoma City, OK 73125 11. Contract or Grant No.

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

FAA Office of Aviation Medicine

Federal Aviation Administration

800 Independence Avenue, SW.

Washington, DC 20591 14. Sponsoring Agency Code

15. Supplemental Notes

This work was performed under task # AM-A-HRR 519-99.

16. Abstract

Thirty-six pilots were tested in a flight simulator on their ability to decide which of two airports was farther

from a storm front, based on the manner in which information was presented on a navigational display. The

results support the superiority of graphical over textual information display of nearest airport information.

Pilots were significantly faster using the map display than using either the text-only display or the enhancedtext display. In addition, in contrast to an earlier study (Williams, 1999), pilots performed better using a

north-up map than when using a track-up map. Discussion of the results focuses on recommendations for

moving-map displays and the display requirements for support of the nearest-airport function within a

navigational display.

17. Key Words 18. Distribution Statement

Aircraft Navigation, Human-Computer Interface,

Aircraft Displays, Pilot Performance

Document is available to the public through

the National Technical Information Service,

Springfield, Virginia 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 16

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

iii

ACKNOWLEDGMENTS

This research is part of the Civil Aeromedical Institute General Aviation Human

Factors Research Program. Program direction is provided by the Aircraft Certification (Small

Aircraft Directorate, ACE-100) and General Aviation and Commercial Division (AFS800) sponsors.

The author expresses his appreciation to Nicole Nelson for her help in preparing the

experimental scenarios and in the data collection process, and to Howard Harris for his

help in recruiting subjects.

1

COMPARING TEXT AND GRAPHICS

IN NAVIGATION DISPLAY DESIGN

INTRODUCTION

Since the advent of graphics-capable computer

systems there has been a question of whether graphically presented information is more effective than

information presented in a textual format (DeSanctis,

1984; Tullis, 1981). The types of tasks tested have

varied from data base retrieval (Boehm-Davis, Holt,

Koll, Yastrop, & Peters, 1989) to military tactical

decision making (Wickens & Scott, 1983). While

common opinion might support the superiority of

graphically presented information, it is interesting to

note that not all of the empirical data show a clear

advantage of graphically presented information over

textually presented information. Nawrocki (1972),

for example, found no significant advantage to either

graphics or text when subjects were required to remember previously presented information. In addition, research examining the performance on

procedural tasks as a function of whether instructions

are presented verbally, graphically, or in combination

has shown that pictures alone often lead to quicker

completion times on procedural tasks, but words lead

to greater accuracy (Booher, 1975; Rigney and Lutz,

1976; Stern, 1984).

Tullis (1981) suggested that the main conclusion

to be drawn from a review of these studies is, not

surprisingly, that the effects of graphics on human

performance are highly dependent upon the task. It is

useful, therefore, to ask what task factors influence

this performance. Wickens and Scott (1983) identified two factors that might influence the effectiveness

of graphically versus textually presented information. The first factor is the compatibility between the

stimulus, the cognitive processing, and the response

required for the task (or S-C-R compatibility). That

is, if the information displayed (the stimulus) matches

or corresponds to the type of processing and response

required for the task, then the task will be performed

more quickly and effectively than if no such compatibility exists. Wickens, Sandry, and Vidulich (1983)

proposed that tasks that demand spatial/analog processes in working memory will be best served by

visual spatial displays and more poorly served by

textual displays.

A second factor suggested by Wickens and Scott is

the degree to which several pieces of information can be

presented in a simultaneous, integrated format. For

example, two different pieces of information can be

displayed graphically as the height and width of a

rectangle. The area of the rectangle could then be

perceived in an integral fashion so that both pieces of

information are processed simultaneously. The relative

importance of both of these factors is undecided (see

Boehm-Davis et al., 1989).

The question of graphically versus textually displayed information was recently studied in the context of navigational display design (Williams, 1999).

Most navigational displays found in General Aviation (GA) aircraft today are used in combination with

global positioning system (GPS) units. GPS units

have a function for displaying the nearest waypoints

to the current position of the aircraft. The types of

waypoints that can be displayed include very high

frequency omnirange (VOR) facilities, nondirectional

beacons (NDB), navigation intersections, and airports. The use of the nearest waypoint function for

the display of nearest airport information is relevant

to pilot safety considerations, since this information

would likely be used under emergency and/or distress

conditions.

In most current GPS units, nearest airport information is displayed in a text-based format, even if the unit

contains a moving-map display. The information usually given to the pilot includes the airport identifier,

bearing to the airport, and distance to the airport, for the

closest 10 to 20 airports from the current aircraft

position. The decision to display this information in a

textual format is most likely based on programming

convenience (Boehm-Davis et al., 1989).

Since many GPS units have a moving-map display,

it is possible to present airport distance and bearing

information directly on the moving map, rather than

in a text-based tabular format. Williams (1999) asked

participants to judge the relative bearing to the nearest airport. Nearest airport information was presented in either a tabular, text-based format, or directly

within a moving-map display. In addition, a third
2

condition involved a text-based format that included

an orienting symbol next to each airport identifier.

For the map-based condition, the map was oriented

either in a north or track-up manner.

Results from the study showed that the use of the

tabular, text-only format normally found on such

displays was significantly slower and less accurate

than either a map display of nearest airport information or the text display that included the orientation

symbol. In addition, it was found that participants

were faster and more accurate with the track-up map

display than with the north-up map display at indicating the relative bearing to the nearest airport.

Another important finding from the study was that

pilots tended to ignore information available from

the heading indicator, and instead focused solely on

the GPS display to perform the task.

The results indicated that the graphical display

had both the advantage of S-C-R compatibility with

the required task (which was essentially a visualization of the relative bearing to the airport) and an

advantage due to the integration into a single presentation of current aircraft heading and bearing to the

nearest airport. Furthermore, since the advantage

possessed by the graphical display was eliminated

when an orientation symbol was included in the text

display, it seems that, at least for this task, the

integration factor was more important than S-C-R

compatibility. This conclusion is based on the assumption that the orientation symbol, as with the

map display, integrated the current aircraft heading

and bearing to the airport into a single presentation.

Several questions arose from the results of Williams (1999) that bore further study. One question

was in regard to the type of task that was performed.

Participants in the original study were required to

make an ego-referenced judgment as to the relative

direction of the nearest airport (see Williams, 1999

for details of the task). Under the text-only condition, this task required the participants to integrate

information about the current aircraft heading and

the absolute bearing to the nearest airport. If the task

were changed from one requiring an ego-referenced

judgment to one requiring a world-referenced judgment (Harwood &Wickens, 1991; Hooper & Coury,

1994; Wickens, 1992), there would be no need to

integrate heading and bearing information. This could

possibly eliminate the advantage demonstrated by

the map-based display over the text-only display. It

would also eliminate the advantage of the enhancedtext display. In addition, changing the task from one

requiring an ego-referenced judgment to one requiring a world-referenced judgment would favor the use of

a north-up map over a track-up map (Wickens, 1992).

A second question from the original study concerned the type of participants used in the study. The

original study used both certificated pilots and nonpilots. Results from the study demonstrated that the

non-pilots were significantly slower than pilots at

performing the task. Eliminating non-pilots from the

study might also eliminate the significant advantage

of the graphic display over the text-only display.

A third question concerned the focus of attention

of the pilots during interaction with the GPS display.

Pilots tended to focus solely on the GPS display

during the 5 to 10 seconds required to complete the

orientation task. Because of the stability of the simulation, this was not a problem as far as the flight path

of the aircraft was concerned. However, if the simulation were less stable, possibly through the use of a

turbulence model, a 5 to 10 second lapse of attention

away from the flying task could lead to much more

noticeable effects on the flight path of the aircraft.

The present experiment was designed to answer

these questions. The task was changed from one

requiring an ego-centered judgment (deciding the

relative direction to the nearest airport) to one requiring a world-centered judgment (deciding which of

two airports was furthest away from an approaching

storm front). As in the original experiment, three

display types were tested. These types were a textonly, tabular presentation of nearest airport information, a text-based display that included an orientation

symbol (called the enhanced-text display), and a

graphical, map-based presentation. Refer to Figures

3-5 for depictions of these three display types.

A second variable manipulated was the map display type. The map display was shown in either a

north-up or a track-up configuration. For the enhanced-text condition, the orientation symbol showing the position of each airport was relative to the

current aircraft heading or relative to north. A third

variable manipulated in the study was the direction of

travel for the aircraft. The plane was heading either

relatively north (i.e., between a heading of 345 degrees and 015 degrees, inclusive) or relatively south

(i.e., between a heading of 165 degrees and 195

degrees, inclusive).
3

A final variable of interest was the level of turbulence present during the task. It was suspected that if

pilots did not attend to the flying task while interacting with the GPS display, the presence of turbulence

would not affect the amount of attention required to

interact with the GPS display. On the other hand, if

pilots did attend to flying while interacting with the

GPS display, the presence of turbulence should increase the overall workload and lead to noticeable degradations in performance with the GPS decision task.

METHODS

Participants

Thirty-six participants were recruited from the Oklahoma City metroplex area. Thirty-three participants

held current private pilot certificates, and three were

currently completing flight training for a private pilot

certificate. Pilots were recruited from local fixed-base

operations (FBOs). All participants were paid. Information was collected regarding participants’ education

level, gender, flight experience, age, handedness, and

GPS experience. Among the participants, only two were

female. The median number of flight hours of the group

was 295, ranging from 7 to 11,000 hours. Twenty of the

thirty-six pilots, or approximately 56%, had experience

using a GPS unit.

Facilities

Data collection was performed using the Basic

General Aviation Research Simulator (BGARS) located at the FAA Civil Aeromedical Institute in

Oklahoma City. BGARS is a medium-fidelity, fixedbase, computer-controlled flight

simulator. The controls and displays used in the BGARS for this

study simulate those of a Beech

Sundowner. Control inputs are

provided by high-fidelity, analog

controls, including a damped and

self-centering yoke, navigation

radio frequency selection module, rudder pedals, throttle, gear,

flap, and trim controls. Instruments are displayed on a Cathode

Ray Tube (CRT) and react in real

time to control inputs and aircraft conditions. The external

views consist of a 50-degree

forward-projected view, two

smaller right-side-view CRTs, and two smaller leftside-view CRTs. A GPS display was hosted on a 10-

inch, True PointTM, touch-screen panel located just

to the right of the pilot position and within easy reach

of the pilot. Participants interacted with the panel

using only their right hand. Figure 1 shows the

BGARS setup with the touch-screen panel located in

the lower right-hand corner of the picture.

Experimental Design

Four factors were manipulated in the experiment:

1) nearest airport information display mode (textonly display, enhanced-text display, map display); 2)

map display mode (north-up or track-up); 3) aircraft

heading (generally north or generally south); and 4)

turbulence (on or off), resulting in a 3 x 2 x 2 x 2

experimental design. All conditions were manipulated within-subject. Dependent variables that were

collected were decision time, decision accuracy (i.e.,

selecting the correct airport), and navigational accuracy (i.e., deviation from the assigned heading at the

end of the trial).

Design of Trials

Four aircraft headings were used in the experimental trials. Two headings were for the generally north

condition (345 degrees and 015 degrees), and the

other two headings were used in the generally south

condition (165 degrees and 195 degrees). In addition, four pairs of airports were selected from a

navigational chart of the Oklahoma area for use in the

experiment. Two of the airport pairs were located east

and west of each other. The other two pairs were

Figure 1: The Basic General Aviation Research Simulator.
4

located north and south of each other. Each airport

was approximately 20 miles from its paired airport. No

airport was located close to a large metropolitan area.

For each airport pair and for each aircraft heading,

four aircraft positions were selected that met the

following conditions: 1) the position was approximately halfway between both airports but at least two

miles closer to one airport than the other; and 2) the

direction to the closest airport corresponded to one

of four clock directions relative to the aircraft, consisting of either the 1, 4, 7 or 10 o’clock positions or

the 2, 5, 8 or 11 o’clock positions. Relative clock

directions were defined such that 12 o’clock was

directly in front of the aircraft and 6 o’clock was

directly behind the aircraft, with all other clock

positions relative to these. For two of the airport

pairs, the clock directions were 1, 4, 7 and 10 o’clock,

for the other two pairs, the clock directions were 2, 5,

8 and 11 o’clock. The total number of positions

selected was 4 (airport pairs) x 4 (headings) x 4 (clock

positions) = 64 positions. From these 64 positions,

48 were selected at random for each subject to be used

during the experiment. The positions were selected

randomly with the constraints that half were north

and half were south aircraft headings, and for half of

the north and south trials the relative direction of the

nearest airport was in front of the aircraft (the 1, 2,

10, or 11 o’clock positions); for the other half, the

relative direction of the nearest airport was behind

the aircraft (the 4, 5, 7 or 8 o’clock positions).

Procedure

Participants were tested individually. Each participant received a consent form to read and sign and

then completed a questionnaire. Questions determined the participant’s age, gender, handedness,

educational level, flight experience, and GPS experience. After completing the questionnaire, the participant was seated at the simulator, and an explanation

of the experimental task was presented. During the

actual experiment, presentation of trials was grouped

by presentation mode (text, map, enhanced-text)

within map mode (track-up, north-up). Participants

received ten practice trials on a particular presentation mode and then were given four actual trials for

that mode during the first half of the experiment.

During the second half of the experiment, participants received two practice trials on a particular

mode and then were given four actual trials for that

mode. Within each set of four actual trials, the order

of northbound and southbound trials was random.

For two of the four tasks within each presentation

mode, turbulence was added to the simulation, making the flight dynamics unstable and requiring more

extensive control inputs to maintain a particular

heading and altitude. In all, 36 practice trials were

completed, along with 24 actual trials, making a total

of 60 trials for each subject. The order that participants received presentation and map mode conditions was counterbalanced.

Following completion of the experimental task,

participants were debriefed and asked which of the

experimental conditions they preferred and whether

or not they made use of the orientation symbol

during the enhanced-text condition. Their preferences were recorded, and they were then dismissed.

Decision Task

Figure 2 shows an example of the GPS display

(north-up map mode) at the beginning of each trial.

Under the track-up map mode, the airplane symbol

pointed straight up and the current aircraft heading

was shown in the center box above the moving-map

display (in place of the large “N”). Participants flying

the simulator were asked to maintain the course

shown on the display. In addition, they were asked to

descend or climb to 3000 feet MSL, from a starting

altitude of either 2500 feet or 3500 feet MSL, and

then to maintain that altitude during the remainder

of the trial. No airports were shown on the movingmap display until after the nearest airport function

had been activated to prevent participants from beginning the judgment task early. Note that, regardless of the display condition used for the trial, pilots

were shown a moving map display in either a trackup or north-up orientation prior to the judgment

task. This included the text and enhanced-text conditions. The actual judgment task began when a large

red “EMERGENCY” message appeared just above

the airplane symbol, accompanied by a steady beeping from the computer speaker, which was the indication for the pilot to begin the task.

Pilots were asked to perform a three-step judgment

procedure. The first step was to press the “NR”

button on the display to bring up the nearest airport

information. The second step was to note the information at the bottom of the display indicating the

position of an approaching storm front. Based on this

information, and the locations of the two airports,

the third step was to decide which of the two airports
5

Figure 3: Text-only method of presenting nearest airport information.

Figure 2: Example GPS display at the beginning of each trial (north-up map mode)
6

was farther from the approaching storm front and to

indicate this by touching the airport, or its identifier,

on the touch-screen panel. For the text conditions,

this meant touching anywhere along the line of text

for that airport (see Figure 3 for a depiction of the

airport information on the text display). For the map

condition, this meant touching the airport symbol

itself on the moving-map display (see Figure 5 for a

depiction of the airports on the moving map display).

After the pilot touched one of the two airports on the

display the trial ended and the next trial was immediately begun.

Nearest airport information was presented in one

of three ways. The first method, shown in Figure 3,

was called the text-only method. In this method, the

nearest airports were listed in a tabular format on the

screen with the airport identifier, bearing to the

airport, and distance to the airport shown. An asterisk was positioned next to the closest airport. In the

example shown in Figure 3, the aircraft is on a

heading of 165 degrees. The nearest airport, OK09,

is at a bearing of 212 degrees, southwest of the

aircraft. The other airport, F61, is at a bearing of 159

degrees, southeast of the aircraft. The pilot, after

noting that the message at the bottom of the display

indicates that the storm is approaching from the east,

would touch the line of text for the airport located to

the southwest, airport OK09.

The second method for presenting nearest airport

information is shown in Figure 4. Known as the

enhanced-text method, this method is similar to the

text-only method, with the exception of an additional symbol located to the right of the airport

information. This symbol is an indication of the

direction to each of the airports listed. When the

display was configured in a north-up mode, the

symbol corresponded to the compass bearing to the

airport. When the display was configured in a trackup mode, the symbol corresponded to the relative

direction (from the current aircraft heading) to the

airport. In the example shown in Figure 4, the aircraft

is on a heading of 015 degrees. Airport 3F7 is at a

bearing of 135 degrees. Airport H01 is at a bearing of

201 degrees. The storm front is approaching from the

east. The pilot in this example should select the

airport farther to the west, or H01.

The third method for presenting nearest airport

information is shown in Figure 5. In this method, the

nearest airports are shown directly on the map display, with an asterisk positioned next to the closest

airport. In the example shown, the aircraft is on a

heading of 165 degrees. The nearest airport, OK09,

is at a bearing of 240 degrees and airport F61 is at a

bearing of 145 degrees. Because the storm is approaching from the east, the pilot should select airport OK09 by pressing it on the touch screen.

For each of the trials, three performance measures

were collected. One was the accuracy for selecting the

airport located farther from the approaching storm

front. A second was the response time required to

make that decision. The third was the difference

between the required aircraft heading and the actual

aircraft heading at the end of the trial.

RESULTS

Decision Errors

All statistical analyses were performed using a

significance threshold of 0.05. A 3 x 2 x 2 x 2 analysis

of variance was performed on the number of decision

errors committed by participants under each experimental condition. A decision error, for purposes of

the experiment, was the selection of the airport closer

to the approaching storm front, rather than the one

farther away. The only factor to reach significance

was the direction of travel, F(1, 35) = 8.566, p =

0.006, MSE = 0.418. Significantly more decision

errors were committed when the aircraft was traveling in a southerly direction than when traveling in a

northerly direction (40 vs. 21 errors respectively). No

other main effects or interactions reached significance. However, several of the tests approached significance. These included the main effect due to map

mode (north-up vs. track-up) F(1, 35) = 3.007, p =

0.092, MSE = 0.260; the map mode by display mode

(text, graphics, enhanced-text) interaction, F(2, 70)

= 2.676, p = 0.076, MSE = 0.181; the map mode by

direction of travel interaction F(1, 35) = 3.026, p =

0.091, MSE = 0.196; the direction of travel by

turbulence factor (turbulence on vs. turbulence off)

interaction, F(1, 35) = 3.718, p = 0.062, MSE =

0.140; and the four-way interaction between all factors, F(2, 70) = 3.034, p = 0.054, MSE = 0.130.
7

Figure 4: Enhanced-text method for presenting nearest airport information.

Figure 5: Map method for presenting nearest airport information (north-up mode).
8

In all, 61 decision errors were committed. Table 1

provides a breakdown of the errors by each of the

factors.

While none of the overall statistical analyses reflects the result, it is important to note that only two

of the 61 errors were committed under the north-up

map condition (see table above). More than six times

as many errors (13) were committed in the comparable track-up map condition. A paired t-test was

performed comparing the north-up and track-up

map conditions only. Results showed that significantly more errors were committed under the trackup map condition, t(35) = 3.179, p = 0.003. The

greatest number of errors (16) was committed under

the track-up enhanced-text condition. In this condition, the airplane symbol pointed to the relative position

of the airport from the current aircraft heading.

Decision Time

A 3 x 2 x 2 x 2 analysis of variance was performed

on the time between presentation of nearest airport

information until an airport was indicated by touching the touch-screen panel. Decision time was measured in milliseconds.

A significant effect was found for the map mode

variable, F(1, 35) = 28.47, p < 0.001, MSE = 2.49E+08.

Pilots were faster at deciding which airport was farther from the storm front under the north-up condition (4.27 seconds) than under the track-up condition

(5.34 seconds). A significant effect was also found

due to the type of display, F(2, 70) = 25.061, p <

0.001, MSE = 1.58E+08. Pilots were faster using the

map display (3.94 seconds) than using either the textonly display (5.21 seconds) or the enhanced-text

display (5.25 seconds). In addition to these main

effects, a significant interaction was found between

the map mode and display type, F(2, 70) = 4.744, p

= 0.012, MSE = 26,657,085. No other main effect or

interaction was significant; however, the main effect

due to direction of travel of the aircraft approached

significance, F(1, 35) = 3.465, p = 0.071, MSE =

15,412,044. The presence or absence of turbulence

did not have any significant effect on decision time

for any of the conditions.

Figure 6 shows the interaction between display

type and map mode on response time. As can be seen

from Figure 6, the significant interaction effect is

primarily due to slower response times using the

track-up map for the map and enhanced-text conditions, but not for the text-only condition. Post-hoc

analyses using paired t-tests confirmed this finding,

demonstrating a significant difference between the

track-up and north-up modes using the map display,

t(35) = -6.648, p < 0.001, SD = 1496.37, and between

the track-up and north-up modes using the enhancedtext display, t(35) = -2.954, p = 0.006, SD = 2268.59,

but not between the track-up and north-up modes

using the text-only display, t(35) = -1.651, p = 0.108,

SD = 1612.33. By far, the fastest decision times were

for the north-up map display.

Table 1: Decision errors breakdown

Map Mode

Direction of

travel Turbulence Display Mode

E-Text Graphics Text Total

N-up North Off 1 1 2 4

N-up North On 2 0 4 6

N-up South Off 3 0 4 7

N-up South On 3 1 2 6

Total 9 2 12 23

T-up North Off 3 1 0 4

T-up North On 3 3 1 7

T-up South Off 7 6 3 16

T-up South On 3 3 5 11

Total 16 13 9 38

Grand Total 61
9

Flight Error

A 3 x 2 x 2 x 2 analysis of variance was performed

on the difference between the intended and the actual

aircraft heading at the end of each trial. During each

trial, pilots were instructed to follow a path depicted

on the GPS display. The path was always a straightline course. The difference between this intended

heading and the actual aircraft heading at the end of

the trial is referred to as flight error.

The analysis revealed a significant effect due to

map mode, F(1, 35) = 4.361, p = 0.044, MSE =

142.594. Pilots exhibited less flight error under the

track-up condition than under the north-up condition. This finding replicates other work showing that

track-up displays better support flight path guidance

than north-up displays (e.g., Wickens, Liang, Prevett,

& Olmos, 1996). The analysis also showed a significant effect due to turbulence being present or absent

during the trial, F(1, 35) = 18.637, p < 0.001, MSE

= 943.76. Not surprisingly, flight error was higher

under turbulent conditions.

Post-test Questions

Following the completion of the experimental

trials, pilots were asked two questions regarding

which display type they preferred the most and whether

or not they used the enhanced-text symbology during

the decision task. Twenty-four of the thirty-six pilots

(67%) stated that they preferred the north-up map

display for performing the decision task. Four (11%)

expressed a preference for the track-up map display.

Six of the pilots (17%) stated they liked both map

displays equally. One of the pilots preferred the

north-up map and the enhanced-text display with the

north-referenced airplane symbol equally. One pilot

expressed equal preference for the track-up map and

the enhanced-text display with the heading referenced airplane symbol.

Regarding actual use of the airplane symbol under

the enhanced-text condition, 18 of the pilots (50%)

stated that they did not use the symbol at all but

instead, relied solely on the airport bearing information (making this condition equivalent to the textonly condition for those pilots). Of the pilots who

used the enhanced-text symbology, six stated that

they only used the symbol when it was north-referenced. One pilot stated that the symbol was used only

when it was heading-referenced.

DISCUSSION

The results of this experiment, support the previous one (Williams, 1999), regarding the superiority

of graphical over textual information display of nearest airport information. Pilots were significantly faster

using the map display than using either the text-only

display or the enhanced-text display. In addition, the

fewest errors occurred under the graphical display

condition. These results lend support to the notion

that tasks that demand spatial/analog processes in

2000

3000

4000

5000

6000

Etext Map Text

Display Type

Decision Time (ms)

North-Up

Track-Up

Figure 6: Decision time as a function of display type and map mode.
10

working memory will be best served by visual spatial

displays (Wickens et al., 1983). Unlike the previous

experiment, however, the inclusion of an orientation

symbol in the text display did not eliminate the

advantage shown by the graphical display. There are

several reasons why this occurred. First, the task of

selecting the airport farther from the approaching

storm front did not require integrating the current

aircraft heading with the bearing to the airport.

Because no integration was required, the only advantage offered by the symbol was that it acted as a visual

representation of the bearing to the airport under the

north-up condition. Under the track-up condition,

the symbol represented relative bearing to the airport,

and for purposes of the decision task, offered no

useful information to the pilot.

Second, only half of the pilots reported actually

making use of the orientation symbol. Some pilots

thought the symbol was confusing. This confusion

could have been due to changing the symbol during

the experiment between indicating the relative direction of the airport to indicating the absolute bearing

to the airport. Other pilots stated that they preferred

using the bearing information to the airport to make

their judgments and did not even attempt to use the

orientation symbol. Again, as with the previous experiment, more practice with the orientation symbol

could alter these results.

Besides eliminating the advantage shown by the

orientation symbol in the enhanced-text condition,

the other result of changing the task from an egoreferenced judgment to a world-referenced judgment

was to cause the north-up map mode to be more

effective than the track-up map mode. Not only was

it found that pilots responded significantly faster

under the north-up condition than the track-up condition, but post hoc analysis revealed that far fewer

errors were committed under the north-up map condition than under any of the other conditions.

Wickens, Liang, Prevett, & Olmos (1996) advocate the use of a track-up map as the default option of

any computer-based map display to be used for navigation. However, this recommendation assumes that

the primary navigational use of such a display would

be to maintain lateral and vertical position along a

course. Indeed, this experiment replicated the finding that a track-up display is more effective for lateral

tracking than a north-up display. It is unlikely, though,

that either a track-up or north-up map display would

be used for real-time course guidance during flight.

Instead, real-time course guidance would be provided either by a traditional course direction indicator or, in future systems, by some sort of

highway-in-the-sky display (Reising, Liggett, Kustra,

Snow, Hartsock & Barry, 1998).

The inclusion of only pilots in the present experiment demonstrated that experience using heading

and bearing information does not eliminate the advantage that a graphical display of that information

provides. Evidence that both the speed and accuracy

of decisions can be affected by the choice of display

formats was found in the current study. While some

of the pilots expressed a preference for the text-based

formats, most preferred the map-based display. In

addition, while some preferred the track-up map

display, most thought that the north-up display was

the easier to use and most effective for the task that

was performed.

The presence of turbulence did not have much

effect on decision performance. This was evident in

the lack of any significant interactions between the

turbulence factor and any of the other factors. In

contrast, though, there was a significant effect on

flight error due to turbulence. Rather than expending

additional resources on controlling the aircraft under

turbulent conditions, pilots may have focused their

attention on interacting with the display. If true, this

outcome is consistent with previous research demonstrating that pilots tend to ignore flying the aircraft

while interacting with the GPS display (Williams,

1999; Wreggit & Marsh, 1998).

Most, if not all, current manufacturers of GPS

units have elected to present nearest airport information in a text-only format. Sometimes this information is presented in a tabular form that allows

comparison among several alternatives, but other

times each airport is presented one at a time, starting

with the closest airport. The most likely reason that

the information is presented only textually is a matter

of precedence. The design of GPS units was based on

the design of earlier systems used for area navigation

(i.e., Loran). Because these earlier systems were designed at a time when display capabilities were more

restricted, all information was presented as text-only.

As new display capabilities arrived, added functionality took advantage of these capabilities; however,
11

the format for the nearest airport function was already established. This suggests that the next generation of navigational displays will continue propagating

design decisions made for older displays and that

only new functionality will take advantage of the new

display capabilities. Integrated displays will make it

possible to have weather, traffic, and terrain information available simultaneously to the pilot. This integration should allow presentation of nearest airport

information in a graphical format that will include

weather, terrain, and traffic. Such a presentation

format would improve the decision-making process

and allow more useful information to be included in

the decision, but only if designers of new displays are

willing to abandon previous display design decisions.

For now, the following recommendations can

be made regarding the display of nearest-airport

information:

• Nearest-airport information should be presented

in a format that best supports the types of decisions to be made with this information. Based on

the current study and previous research (Williams, 1999), the best format is a graphical format

in which relative and absolute direction and distance can be determined from among a small set

of alternatives.

•In the absence of integrated graphical weather,

terrain, and traffic displays, the use of a north-up

map is superior to a track-up map for orienting to

world-referenced obstacles.

• Use of a track-up presentation might be acceptable for orienting to world-referenced obstacles if

an intuitive and easily interpreted way to indicate

cardinal directions were present within the display.

• Use of a track-up map is superior when orienting

to self-referenced obstacles. An example of this

would be orienting toward the runway during

conduct of an instrument approach.

•The use of graphical symbols within a text display

can improve the usefulness and effectiveness of

the display but a certain amount of training will

be needed with the display before it can be used

efficiently.

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