Ye Hong, Henry Martin, and Martin Raubal
of individual travel behaviour, such as the availability of travel
modes [
27
] and the day of the week [
7
]. However, the comprehen-
sive information regarding individuals’ travel behaviour is not fully
utilized in location prediction problems. To date, it is still unclear (1)
how strong the inuence of these long-term factors is on choosing
the immediate next location and (2) whether the DL network can
benet from this knowledge and learn the complex dependency
patterns directly from data.
To close this research gap and answer the above questions, we
propose a transformer-based model that utilizes historical travel
behaviour to predict individuals’ next location. More precisely, the
model aims to learn mobility transition patterns from historical
location, temporal and travel mode sequence information. Inspired
by travel behaviour studies, we encourage the model to also pre-
dict the next travel mode the individual will choose. We anticipate
that this ancillary task will help the prediction of the next loca-
tion. Through experiments on two real-world GPS datasets, we
demonstrate the eectiveness of our model design and quantify
the dependency of location prediction performance on travel mode.
Our results show that careful consideration of individual travel be-
haviour signicantly benets human mobility prediction. In short,
our contributions are summarized as follows:
•
We propose a transformer decoder-based neural network
that utilizes location, travel mode and time-related infor-
mation for the next location prediction task. The proposed
model achieves state-of-the-art performance.
•
We show that jointly learning the next location and next
mode improves the prediction performance for both tasks.
•
We conduct extensive experiments on two real-world GPS
tracking datasets and conclude that considering additional
aspects of travel behaviour signicantly increases the per-
formance of next location prediction.
The rest of this paper is organized as follows. We rst systemati-
cally review related work in Section 2. In Section 3, we formulate
the next location prediction problem. Next, we introduce details of
the network architecture in Section 4. We apply our model to two
real-world GPS datasets and analyze its performance in Section 5.
Finally, we summarize the main ndings and conclude the paper in
Section 6.
2 RELATED WORK
2.1 Next location prediction
The next location prediction problem has found application in many
dierent elds, such as recommendation systems [
44
], sensor net-
works [
28
], and mobility behaviour analysis [
41
,
42
]. The exact
denition of the problem varies across studies due to dierent ob-
jectives and employed datasets. For example, location-based social
network (LBSN) applications focus on predicting the next check-
in point-of-interest (POI) [
40
,
44
]. In contrast, mobility behaviour
studies aim to understand the next location for a user to conduct an
activity [
34
]. Here we focus on the methods proposed for mobility
applications.
The last decade has witnessed the expansion of studies focus-
ing on next location prediction. Markov Chain and its variants are
probably the most often employed methods for the task [
22
]. These
models regard locations as states and construct a transition ma-
trix that encodes the transition probability between states for each
individual. Ashbrook and Starner
[1]
and Gambs et al
. [11]
both
proposed identifying signicant locations from GPS data and build-
ing a Markov model to predict location transitions. Later Markov
model variants that consider collective movements [
3
] and incor-
porate location importance [
17
] further increased the prediction
performance. However, Markov-based models struggle to represent
the complex sequential patterns in human mobility because of their
inherent assumption that the current state only depends on the
states of previously limited time steps [20].
Recent advances in DL have also promoted their application
in location prediction. As a widely adopted sequence modelling
method, recurrent neural network (RNN)-based models, such as
Long Short-Term Memory (LSTM) [
34
] and spatial-temporal (ST)-
RNN [
21
], were reported to outperform Markov models by a large
margin in the task. Still, vanilla RNN models tend to underweight
long-term dependencies when the input sequence length increases.
Therefore, studies employed the attention module to capture both
short-term and long-term dependencies dynamically [
9
,
20
]. More-
over, the transformer model that builds on top of the multi-head self-
attention mechanism [
39
] have started to gain interest in the eld.
In particular, Xue et al
. [44]
proposed MobTcast for considering
various contexts with a transformer-based structure and achieved
state-of-the-art POI prediction results for LBSN data. Although
having great potential in learning the complex spatio-temporal
dependencies, limited studies have applied transformer for the lo-
cation prediction problem.
2.2 Factors aecting activity location choice
Understanding the factors aecting activity location choice is bene-
cial for predicting individuals’ mobility, as they can be regarded as
prior knowledge and potentially guide the learning of DL models. In
the travel behaviour eld, the choice of locations is regarded as an
integral part of individuals’ activity-travel behaviour and has been
studied within the activity-based framework [
32
]. Studies that focus
on analysing travel behaviour over time suggest that both stability
and variability are found in individuals’ activity location choices.
For example, Dharmowijoyo et al
. [6]
showed that the variability
of location visits is much larger between weekend-weekday pairs
than between weekday-weekday and weekend-weekend pairs. Em-
pirical studies also demonstrate the correlation of dierent aspects
of individual travel behaviour. For example, Susilo and Axhausen
[38]
reported high repetition in location-mode combinations, sug-
gesting that individuals use the same travel mode to reach their
locations. Similar conclusions were reported by Hong et al
. [14]
,
where they found that only a subset of all location-mode combi-
nations is essential for describing the mobility behaviour. From
this perspective, aspects of travel behaviour can be considered
constraints for individuals’ choice of activity locations.
A similar problem as the next location prediction is the for-
mulation of an individual’s location choice set, which is a crucial
component in microscopic trac simulation models [
19
]. Instead of
predicting the exact next location, the problem aims at generating
a set containing all possible locations. Based on time geography
theory, potential path areas analysis has been applied to tackle