Potential-of-Interest Maps for Mobile Tourist
Information Services
Yohei Kurata
Department Tourism Science
Tokyo Metropolitan University, Japanykurata@tmu.ac.jp

Abstract
To prevent tourists from being overwhelmed by a flood of tourist information, this paper
proposes an alternative approach to tourist information services, namely potential-of-interest
maps. Potential-of-interest maps visualize the sightseeing potential of each place in a tourist
area, which is estimated from data about locations where previous visitors have foundsomething impressive. Such maps provide visual aids for tourists and will save their effort at
decision making. In this paper, we first compare five possible approaches for obtaining data
about locations where previous visitors have been impressed, among which the use of photogeo-tags is concluded the most promising. We then construct an example of potential-ofinterest maps making use of Flickr’s photo data. Finally, we develop a prototype of a mobile
tourist information tool which features a potential-of-interest map. In our user test, nine of
twelve test users show an intention to use this tool again at other destinations.
Keywords: mobile tourist information services, potential-of-interest maps, photo-taking
locations, kernel density estimation, user participation

1 Introduction
Tourism is an activity in which people need a large amount of information, as it isperformed in unfamiliar environments. For this reason, many engineers andresearchers have undertaken the challenge to provide information aids for tourists,making use of rapidly-advancing mobile information technologies (e.g., Zipf &Manaka 2001). In addition, AR and ubiquitous technologies, which bridge the realworld and information in a more seamless way, are increasing the capabilities ofmobile tourist information services. However, there is also a concern about mobile
tourist information services, because they may confuse tourists by provide too muchinformation through a tiny screen. To tackle this problem, computational techniques
for selecting and reorganizing information based on user profiles, such as
collaborative filtering (Resnick 1994), have been applied to the domain of tourist
information services (for instance, Ricci et al. 2002). However, such techniques
usually require a certain amount of time and effort to obtain the user’s profile. In
addition, depending on destinations and party members, a tourist’s preferences maychange from time to time, which makes the problem more difficult (Kurata 2011).
In this paper, we introduce an alternative approach for mobile tourist information
services, called potential-of-interest maps. Our key idea is to visualize the sightseeingpotential (or potential-of-interest) of places in a tourist area, based on data aboutlocations where previous visitors have found something impressive. The map that
illustrates potential-of-interest is highly useful for tourists, as they can visually
identify which places will be worth visiting and on which route they can enjoy suchplaces efficiently, without reading unnecessary text. In this paper, we discuss how weshould construct such potential-of-interest maps, as well as how we can employ thesemaps in mobile tourist information services. The main contribution of this paper is to
propose a new layer of a tourist map which promotes the users’ visual thinking intheir tour planning, while many of existing tourist information tools depends on
textual information.
The remainder of this paper is organized as follows: Section 2 explains the concept
and merits of potential-of-interest maps in detail. Section 3 compares five possible
approaches for determining locations where visitors have found something impressive.
Section 4 constructs a sample potential-of-interest map, with which we develop a
prototype of a tourist information tool in Section 5. Section 6 reports the result of ouruser test. Finally, Section 7 concludes with a discussion of future work.

2 Potential-of-Interest Maps: A Visual Aid for Tourists
In a potential-of-interest map, each point is painted in deeper colours as more tourists
found something impressive at and around the corresponding location in the realworld. Potential-of-interest maps can achieve a certain level of tourist guides without
textual information. For instance, a deeply-coloured spot probably indicates thepresence of popular tourist attractions there. A linearly-stretched coloured area
probably corresponds to a major corridor where many tourists come and go. Isolated
coloured spots may indicate hidden places-of-interest which attract adventurous
tourists. With such implications, tourists can think visually about where they should
go and which route they should take, without reading unnecessary text.
The absence of unnecessary text, if it is carefully designed, may stimulate users’
inquisitive spirits. People who visit a high-potential location will try to find what isinteresting there, if it is not obvious, by awakening their five senses. Interestingfindings will not only satisfy them, but also make them perceive a sense ofcommunity with previous visitors who have found that place. Such a tourist
information service will attract adventurous tourists who consider other services
officious and noisy.
It is also nice, especially for novice users, to supplement potential-of-interest maps
with certain textual information. For instance, we can develop a digital version of apotential-of-interest map, in which information about each tourist attraction appears
when the user clicks the corresponding point on the map. An important feature ofsuch text-enhanced potential-of-interest maps is that the painted pattern of potentialof-interest helps the users to decide which tourist attractions they should consider intheir tour planning; in other words, they can visually identify which attractions are notworth reading their information. In this way, potential-of-interest maps can be used asbase maps for other tourist information.

3 Calculation and Visualization of Potential-of-Interest
To make a potential-of-interest map for a tourist area, we first need to know visitorinterested locations (the locations where previous visitors found something
impressive) in this area. Here we consider the following five possible approaches for
obtaining visitor-interested locations:i. Annotation
This is a simple and inexpensive survey-based approach, in which tourists are asked
after their sightseeing to point or encircle the locations where they have foundsomething impressive.
ii. On-site manual recording
This is also a survey-based approach, in which tourists are asked to carry a GPSequipped device and record their locations when they find something impressive. One
possible method is to prepare an application for smartphones, which records the geocoordinates when the user taps its display, analogous to giving applause. Anotherpossible method is to apply existing micro-blogs, such as Twitter, in which the user
can post a short message with location data.
iii. Use of photo geo-tags
In addition to GPS-equipped digital cameras, recent smartphones also allow users torecord the locations where they take photos. When photos are taken by tourists withthese devices, their photo-taking locations can be regarded as visitor-interested
locations, because in many cases tourists take photos when they find something
impressive there.
iv. Detection from GPS logs
During a walking tour, tourists typically reduce their speed when they find something
impressive. Thus, by analyzing the trajectory of tourists recorded by GPS-equipped
devices, we can detect visitor-interested locations with some degree of accuracy.
v. Text mining
In this approach, we extract the data of visitor-interested locations from a large
amount of texts in travel blogs and reviewing sites. The extraction of such location
data from text on web pages can be easily performed when the page shows geocoordinates or mailing addresses (Kurashima et al. 2005).
In the next step, we compare these five approaches from the following viewpoints:
On-site workloads

It is not desirable to impose certain workloads on tourists during their sightseeing,
because these workloads distract them and may affect their activities.
Off-site workloads
In annotation, the tourists have to recall the locations that have impressed them andthen find them on a map. This task is difficult and error-prone, especially for people
with low map-reading skills.
Accuracy
Spatial accuracy is a concern with both annotation and text mining, since theseapproaches rely on human memory.
Possibility of commission errors
In detection from GPS logs, such locations as traffic intersections and toilets may be
mis-detected as visitor-interested locations, unless a certain data refinement processusing facility location data is applied.
Possibility of omission errors
In use of photo geo-tags, visitor-interested locations in photography-prohibited areas
are never detected. Similarly, in detection from GPS logs, visitor-interested locations
where tourists cannot stop, such as scenery spots on a highway without lookouts,
cannot be detected. In text mining, visitor-interested locations without any reference
to their addresses are difficult to detect. Finally, on-site manual recording is also risky
because the subjects may forget to record their locations, especially when they are
devoted to sightseeing.
Technical challenge
At this moment there are no well-established techniques that realize detection ofvisitor-interested locations from tourists’ GPS trajectories or their writings. Thus,
detection from GPS logs or text mining are more technically challenging than others.
Device necessity
Survey-based approaches are costly, especially when we have to ask the subjects tocarry certain devices. In addition, the devices’ weight may affect their activities. This,
however, becomes a less important issue, because many tourists nowadays carry theirown smartphones and they can be used for experiments.
Table 1 summarises the above discussion. Which approach we should take depends
on which viewpoints we decide to emphasizes. We, however, concluded that use ofphoto geo-tags is the most promising approach, considering its smallest number ofproblems (note that device necessity seems not critical as stated above). In addition, it
is also nice that use of photo geo-tags imposes less workload on tourists thanannotation and on-site map recording, as photo-taking is a tourists’ natural activity.

On-site manual recording×

Use of photo geo-tags
Detection from GPS logs
Text mining

××

Device necessity

Technical
challenge

×

Possibility ofomission errors

×

Possibility ofcommission
errors

Accuracy

Annotation

Off-site Workload

On-site Workload

Table 1. Comparison of five possible approaches for obtaining visitor-interested
locations from seven viewpoints

×

×

×

×

×

×

×

×

×

Now let us assume that we have already obtained a large dataset of visitor-interested
locations in a tourist area by one of the above five approaches. The next mission is tocalculate the potential-of-interest of each location in this area. For this calculation, we
can use a technique called kernel density estimation (Parzen 1962). Roughly speaking,kernel density estimation is a computational operation in which we assign a small hill
for each data point, called a kernel, and measure the total height of all hills on eachlocation. As a result, a location with a larger number of points around it has a higher
value. Kernel density estimation is, in the original sense, a technique to estimate theprobability distribution of a stochastic process from a large set of samples. If we takethe use of geo-tags approach, for instance, tourists’ photo-taking activities are
considered a stochastic process that follows a certain two-dimensional probability
distribution. This probability distribution should reflect the distribution of sightseeing
potentials.
The estimated probability distribution can be represented by a continuous surface map.
This surface map is sometimes called a heat map in analogy to a thermograph.
Intuitively speaking, this surface map represents the density of sample points (in ourcase, visitor-interested locations) at each location. Thus, the surface map, constructed
via kernel density estimation from a large dataset of visitor-interested locations, isconsidered a potential-of-interest map.

4 Demonstration
As a case study, a potential-of-interest map was made by the use of photo geo-tags
approach in Section 3. Our target was Yokohama, a portside city near Tokyo.
Yokohama’s central area is a popular tourist destination, which attracts more thanforty million tourists in a year.
In order to ease the labour of collecting data about photo-taking locations fromtourists, we used Flickr photos for this study. Flickr (http://www.flickr.com/) is one of
the most popular photo-sharing services on the web and is currently owned by Yahoo!
USA. Flickr has many photos taken by tourists. In addition, Flickr has an open andpowerful API with which we can perform geo-searching of Flickr photos in our own
program. Therefore, Flickr is a suitable data source for collecting data about tourists’photo-taking locations. Indeed, there are already many researches which employ
Flickr’s photo data. For instance, Girardin et al. (2007) and Zheng et al. (2011)
inferred tourists’ movement patterns from spatio-temporal sequences of photo
locations of individual photographers, while Hollenstein and Purves (2010) analyzed
people’s perception of areas in a city from the combination of location data and usergenerated tags of Flickr photos. Use of
In our study, we first developed a JavaScript program which automatically collects
the data of Flickr photos that have been taken within a certain rage of a specified
address. The data include the Photo ID, the location (geo-coordinates) where thephoto has been taken, the owner’s ID, and the owner’s place of residence (country
and city names). With this program, we collected the data of 1061 photos of Central
Yokohama (the photos taken within 3km from Yokohama City Hall). We thenremoved 38 photos taken by local residents, who were probably not tourist photos.
The remaining 1023 photos were taken by 95 people (on average 10.8 photos perperson); 34 live in Japan, 20 in other countries, and the place of the remaining 41
people were unknown.
Then, we imported the location data of these 1023 photos into ArcGIS 8.1 with
Spatial Analyst and carried out kernel density estimation. The resulting map (Fig. 1)
shows higher values at and around major tourist attractions in Central Yokohama,such as Minato-Mirai Waterfront Area, Akarenga Park, Ohsanbashi Wharf, andYokohama Chinatown. This supports our intuition that the location data of Flickr
photos, which include many tourist photos, can be employed as the data source forpotential-of-interest maps.

Bayside Park
StationIntercontinental Hotel

Minato-Mirai
Waterfront Area

Transportation
Terminal

Akarenga
Park
BankART
Studio NYK

Ohsanbashi
Whalf

Noge
Old Town
Yamashita
Park
Yokohama
Stadium

Yokohama
Chinatown

Doll Museum

Fig. 1. A potential -of-interest map of Central Yokohama, made from photo-taking
location data of Flickr photos

5 Potential-of-Interest Map-based Tourist Information Tool
Now that we have an example of a potential-of-interest map, we implemented a
prototype of the mobile tourist information tool discussed in Section 2, which featuresa point-of-interest map. This tool first shows a Google map of Central Yokohama,
which is enhanced with a layer showing the potential-of-interest map (Fig. 2-left). In
this map, the darker areas represent the areas with higher potential-of-interest (i.e., theareas where many tourists have taken photos).
This map also contains blue markers, which represent the locations of major tourist
attractions and train stations. In total 34 markers are prepared for this area. If you
click a marker, a short description and a picture of the corresponding facility are
shown in a balloon (Fig. 2-right). The description contains hyperlinks to the official
site and Wikipedia page of this facility, if they exist.
The screen also shows a button named ‘Start Tracking.’ If this button is on, the map
automatically scrolls such that the user’s current location comes to the centre of themap, together with a circle at the centre which shows possible measurement error of
the current location.
Since this tool was developed with JavaScript and the Google Maps JavaScript API
v3, it can be used on various platforms through web browsers. Its screen layout anduser interface depends on the device, due to the specification of the Google Maps
JavaScript API v3. For instance, on Android smartphones and iPhones, the user canscroll the map using one finger. In addition, on iPhones (but not Android smartphones
at this moment) the user can change the map scale with two fingers.
The most remarkable feature of this prototype is its simplicity. The initial screen
shows almost no text except labels. Nevertheless, the map is informative, as it
visually tells the user which attractions are possibly worth visiting and which are not.
If the user becomes interested in a certain area, he may browse the descriptions of
tourist attractions in that area. These descriptions are valuable to judge quickly
whether the attraction is interesting or not for him. If he needs more information forhis decision, the user can obtain it from external sites via hyperlinks. We consideredthat tourist information tools should not be relying entirely on proprietary information,
as it is difficult to keep updating the information up-to-date within individual tools.

Fig. 2. Screenshots of our mobile tourist information tool which features a potentialof-interest map. The balloon in the right screenshot introduces Kishamichi Promenade,saying “A trans-bay promenade which was built on a former freight railroad. Visit
here if you want to enjoy a nice view of Minato-Mirai Waterfront Area over a bay”.

6 User Evaluation
In order to evaluate the developed tool which featured a Flickr-based potential-ofinterest map, we conducted a user test. In this test, we asked its participants to visit
Central Yokohama and do sightseeing freely for at least two hours using our tool.
After that, we asked them to answer an online questionnaire. We had twelve
participants (eight males and four females; average age was 27.2). Nine participants
used their own smartphones, while other three borrowed the Android smartphones we
prepared.
Table 2 summarizes the major result of our user test. Unfortunately, the averagescores of six evaluation items were not glorious. The major reason was that, as
implied by the large standard deviation (S.D.) values, the participants were divided
into sympathetic and anti-sympathetic groups. Particularly, the three participants whoreported their poor map-reading skills were anti-sympathetic. For instance, theaverage score of Item 1 (ease-of-use) by these three participants was only 2.0. On theother hand, three participants who borrowed our Android smartphones gave a score of
3.4 for Item 1, even though they were not used to the smartphones.
Table 2. Test users’ evaluations of our mobile tourist information tool featuring
a potential-of-interest map (5: highest and 1: lowest, n = 12)
Question

Ave. Score S.D.

1. Did you feel that it was easy to operate the system?

3.5

1.2

2. Did you find any new attractive spots while using the system?

3.1

1.1

3. Did you think that potential-of-interest is reliable?

3.3

1.1

4. Did you think that the information about each point-of-interest, shownin a balloon, was sufficient?

3.5

0.9

5. Do you want to use this tool on smartphones again when you visit otherdestinations?

3.7

1.2

6. Do you want to use this tool again on a PC when you plan a trip at
home?

3.4

1.4

Among the six evaluation items, the average score of Item 2 (new findings) was thelowest. This was probably because most participants have already visited Yokohama
many times. Item 3 (validity of potential-of-interest map) was given low scores by theparticipants who visited Yokohama on rainy days. Our potential-of-interest map

seems unsuitable for rainy days, because it was made from the geo-tags of tourist
photos mostly taken on sunny days. Lastly, Item 5 (use intention in other destinations)and Item 6 (use intention at home) are given high scores by nine and seven of twelve
participants, respectively. This makes us confident of the presence of consumer needsfor our new tool.
We also asked the participants to comment freely on our tool. Some participants gave
positive comments on such features of our tools as the absence of unnecessary textual
information, the presence of potential-of-interest data on unfamiliar districts, and easy
access to the information around the user’s current location. We also foundcomplaints about slow data communication speed, inaccuracy of estimated current
locations, and small displays, which were actually device-side problems (although
there is still room for improvement in our side).
Several ideas for improvement were proposed by some participants. One nice idea
was to prepare several potential-of-interest maps which correspond to different
situations (e.g., day and night, sunny and rainy days, dating and solo trip) and toenable their switching or to represent them with different colours.

7 Conclusions and Future Work
It is difficult for tourists to process a large amount of text-base tourist information forfinding which attractions, streets, and areas are worth visiting. This problem becomes
more serious when the tourists are already at the destination and have to rely on theirmobile device with a tiny screen. This paper, therefore, proposed the use of potentialof-interest maps in mobile devices as a visual aid for tourists. Potential-of-interest
maps allow the tourists to understand the distribution of sightseeing values in a tourist
area and accordingly, help the tourists to select the targets (attractions, streets, andareas) whose information should be looked carefully for their tour planning.
In this paper, we made a potential-of-interest map of Central Yokohama from thelocation data of Flickr photos. Geographic visualization of Flickr’s photo-taking
locations itself is not new, but the use of it as a source of tourist information seems a
new idea. Zanker et al. (2010) also discussed the application of user-generated geotagged information on the Web to the tourism domain, although their focus was to use
such information in extending the framework of information retrieval. On the other
hand, we pursued a new presentation style of tourist information.
One remaining issue in the current approach is that we cannot assure that the photos
we have used are taken by ordinary tourists. Thus, we are planning to revise ourpotential-of-interest map based on photo location data collected from actual tourists.
In addition, in order to keep the potential-of-interest map up-to-date, we are planning
to introduce a ‘user participation’ mechanism, in which photo location data arecollected seamlessly from the users of our tool by building a camera function into ourtool. A benefit of this mechanism is that the result of tourists’ natural actions isutilized for guiding future tourists. Ultimately, we would like to evolve the tool into adynamic system in which its users can see where other users are taking photos at each
moment, because many season- and time-dependent attractions, such as festivals,
flowers, and street performances, take place in a tourist area. Another merit of theuser participation mechanism is that we can consider personalization by collaborative
filtering (Resnick 1994); that is, we can customize potential-of-interest maps for eachuser, based on the photo location data of other similar users who have taken photos atsimilar locations.

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Acknowledgements
We appreciate our students who have participated in our user test and gave us
precious feedbacks. This work was supported by JST RISTEX’s research program on
Needs-oriented Service Science, Management and Engineering (title: Architecting
service with customer participation based on the analysis of customer experience anddesign processes: sophisticating tour design processes as a case study) and JSPS
Grant-in-Aid for Young Scientists (B) 23701030 (title: Construction and applicationof potential-of-interest maps making use of tourists’ photo-taking location data).