The literature on informal participation in sport focuses on the improvement of overall health and wellbeing (Bowler et al.,). We do not separate the terms "sport," "exercise," and "participation" here, because in our view any type of PA is beneficial in terms of having an active and healthy lifestyle in the city. We therefore use the term "physical activity" from here on, following the World Health Organization (WHO) definition: "physical activity refers to all movement including during leisure time, for transport to get to and from places, or as part of a person's work" (WHO,). Children in Finland are encouraged to engage in outdoor play from a young age, going outside in all weathers while at kindergarten (Iivonen et al.,). Furthermore, our case study area, the HMA, has many outdoor play parks, averaging almost one per neighborhood, which is not the norm in many other countries. These parks promote exercise in natural environments whilst honing children's independent mobility through to adulthood (King and Sills-Jones,). However, even though Finns seem to have an ingrained habit of engaging in PA year-round, around 70% of the adult population (over 18 years old) are not reaching the recommended weekly target of >=150 min activity of moderate-to-vigorous-intensity PA (Bennie et al.,).
Kolu et al. point out the economic burden of a sedentary lifestyle in Finland: the total cost of low PA behavior came to approximately $ 3.2 billion in 2017, and the costs attributable to high sedentary behavior totaled around $ 1.5 billion. According to the Finnish Institute for Health and Welfare, around 70% of men and 60% of women in Finland are overweight, meaning that they have a body mass index (BMI) of 25 or more, and a third of the population are obese, having a BMI of 30 or more: a score of 18.5-24.9 is healthy. It was found in a similar recent study conducted by the Helsinki and Uusimaa Hospital District that the annual healthcare costs for an obese person were approximately $ 2,665 (Vesikansa et al.,). Rose et al., in turn, reported that spending two or more hours outdoors helps to prevent children from becoming short sighted in the near future, which also eases the burden on health care. Therefore, the provision of free public spaces that allow the population to be active outdoors is one among many simple and effective ways of improving health and simultaneously lowering the negative costs attached to being inactive. It is suggested in current literature based on PA rates and the impact of the COVID-19 pandemic that there is a general tendency to be less active (e.g., Engels et al.,; Ronkainen et al.,; Semple et al.,). However, according to the Ministry of the Environment there is a strategy to increase the recreational use of natural habitats in Finland as part of Prime Minister Sanna Marin's government program. Survey results have shown that, in fact, the COVID-19 pandemic increased the motivation of Finns to exercise in local nature-based surroundings, whereby almost everyone (96%) enjoys outdoor activities: this adds to the relevance of our article.
Researchers have found it difficult to establish participation rates for informal lifestyle sport (Gilchrist and Wheaton,). PA of this type does not typically go on in a fixed place such as a physical sports facility, hence usual practices such as counting tickets are not possible. Consequently, for this article we focused our analysis on already geolocated Twitter tweets to detect the demand for informal sport by location, meaning that the PA takes place in an informal setting away from physical sports facilities. It should be borne in mind that not all PA takes place by or in green or blue urban spaces, and that street spaces also exist. Finland has a national database of sports facilities (LIPAS,), which also includes informal sports infrastructure comprising street spaces (any location not in green or blue spaces) such as outdoor table-tennis tables and basketball courts. We therefore distinguish between three informal urban PA spaces which are also land cover types: (1) green, (2) blue, and (3) street.
For the purpose of this article we focus on informal PA spaces, given that Finland already has a national open database of sports facilities and their conditions, namely LIPAS (LIPAS,). User demand for formal PA facilities can be tracked by means of ticket purchases or by scanning sports cards, but this is not the case for informal spaces, hence it is more difficult to estimate user demand in each location. Table 1 shows varying definitions of informal sports, and whether they mention the location of the PA. We use the term "sport" rather than "physical activity" because the majority of literature refers to informal sport, the assumption being that participation is informal (Wheaton and O'Loughlin,).
However, as Deelen et al. point out, participation in sport may be within sport clubs, gyms, or public spaces, with a focus on the "settings" in which the sporting activity is located. The authors also suggest that most informal sport goes on in public spaces and natural environments, and we follow this same distinction. In our case this even applies to downhill skiing slopes, which have specific opening times and require entrance tickets but are still classed as informal because the public can choose what time to visit within the specified period. Therefore, even though there is no fixed definition of informal sport, it typically simply means being self-organized. According to Coakley, for example, formal sport is "rule-centered" and informal sport is "action-centered," whereby the latter relies on group decision-making among the participants to be self-sustaining: however, this definition omits individual sports. One variation is that the difference is simply a matter of the frequency and context of participation, whereby formal sport takes place at regular times, requires club membership and involves taking part in organized games and competitions (Kokolakakis et al.,).
On the grounds that the distinction between formal and informal sport is not yet fully adopted in either government or non-government agencies, Jeanes et al. define formal sports as any activities that take place in affiliated sports clubs and within official sports structures, for which participants pay a fee and compete in leagues. They further define informal sports as any traditional sporting activity, such as cricket, football, or basketball, whereby participants do not pay membership fees and play in places such as local parks or community spaces. They omit sports such as surfing, skateboarding, and parkour, which they refer to as a "lifestyle" or "leisure" sport that evolved from resistance to traditional sport. According to Mathisen et al., club sport increased in Finland from 1992 to 2010, and general PA participation expanded with the introduction of new informal sports such as cross fit, hiking, and skateboarding. We focus here on the location of the informal sporting activity, which seems to have been omitted in existing definitions.
Green and blue urban spaces have been gaining traction in academic literature (see Korpilo et al.,; Tan et al.,). It is becoming increasingly common to study how and where people exercise in a city. Locations in which physical activities take place that are scenic and in natural surroundings tend to motivate people to improve their overall wellbeing (Loureiro and Veloso,; Bell et al.,). Finland is a suitable country in which to conduct research on where people engage in PA given the large amount of land used as green and blue spaces. Green areas, specifically forests, comprise more than 75% of the country's land (Ministry of Agriculture and Forestry,). Blue spaces, namely water bodies, are particularly high in recreational value among Finnish citizens. Inland water bodies such as lakes and rivers cover ~10% of the country's total surface area, accounting for 34,539 km2 (Ministry of Agriculture and Forestry,). These two statistics exemplify the suitability of Finland for studying where people exercise outdoors in nature, as even urban spaces are encompassed by both green and blue spaces. According to a survey of around 1,250 residents of Helsinki and Tampere conducted by the Finnish Forest Research Institute, over 80% of them thought that the green spaces improved their residential area, and over 90% said their favorite place was in nature, in a forest, on a shore or in another type of green space (Tyrvainen et al.,). This has led to the term "green exercise," which has recently arisen to emphasize the positive effects of combining PA and exposure to nature (Shanahan et al.,; Mnich et al.,). It also has an effect on people's emotions, particularly when walking or otherwise exercising in a forest environment (de Brito et al.,).
Having included three different types of informal urban space in this article, namely green, blue, and street, we thought it important to understand how others used these terms and what in particular made the PA informal compared with traditional or formal sports. We now turn to our third and final urban space, namely street space. Street-based sports have, in the recent past, been associated with rebellion against more traditional informal sport, encompassing skateboarding or parkour (see e.g., Angel,; Rannikko et al.,). We define street space PA here as any physical activity that does not take place on or around green or blue space, but on asphalt, concrete, or similar hard surfaces, including those on which outdoor open sports parks are built. Outdoor public spaces in Finland have varying uses depending on the season. Gravel parks, for example, are used in summer for boules and football, and in winter for ice skating. There are 943 street workout parks in Finland, of which 326 (35%) are within the HMA (LIPAS,), and there are many more outdoor street PA opportunities ranging from obstacle courses to frisbee golf and workout step hills (Kivisto,). Indoor public sport facilities were forced to close to the public during the winter of 2020-2021 due to the COVID-19 pandemic, and only outdoor public spaces were allowed to remain open. Thus, even under the heavy restrictions related to the pandemic there were still many outdoor-exercise opportunities that allowed the general public to remain active.
Recent research has focused on the impact of the COVID-19 pandemic and the resulting increasingly sedentary lifestyles among the population (Du et al.,; Dunton et al.,; Yamada et al.,; Ronkainen et al.,). There was still access to green space in Helsinki, and as Korpilo et al. found, in fact some forest areas nearby were over-crowded, which had a negative impact upon the environment. Informal sport is not often explicitly mentioned in policies: in Finland, for example, the Sports For All policy is still centered around organized sports focusing on diversity (Ministry of Education and Culture,). It would therefore be useful to know where in urban spaces people are doing their PA. Urban spaces tend to be associated with a decreasing amount of green space and with discouraging people from exercising, which could fuel an increase in sedentary living (Triguero-Mas et al.,). Our focus here, however, is on how urban areas could still give access to a variety of outdoor sports.
A healthy city, as defined in the Zagreb Declaration (WHO Regional Office for Europe,), is one that "provides conditions and opportunities that encourage, enable and support healthy lifestyles for people of all social groups and ages." Li et al. conducted a review to distinguish any differences between green and non-green exercise: they found that green exercise did, in fact, have psychological advantages. Since then, social media has been used as a novel source of data to capture the usage of green space during the COVID-19 pandemic (Fagerholm et al.,; Korpilo et al.,; Cui et al.,). However, these studies omit other urban spaces in which informal PA takes place outdoors in fixed locations, such as outdoor gyms, skate parks, and table-tennis facilities. Moreover, outdoor informal sports such as cycling, kayaking, and walking do not take place in fixed locations. It would therefore be useful for municipalities to know where their populations were engaging in PA.
Geotagged Twitter messages have been successfully used in previous academic studies spanning many research topics, such as for analyzing political events (Tear,) or human mobility (Jurdak et al.,). Huang and Carley refer to Twitter as a useful proxy for understanding people's mobility and social events. Tweets are naturally occurring data, the main purpose of which is not for analysis (Sloan and Morgan,). This makes it potentially more suitable for further analysis given that data collected from online users as a by-product are said to be more reliable than survey or questionnaire data in which people might give false answers (McLaren and Shanbhogue,). Tweets typically include a hashtag (#) alongside a phrase or term, which researchers follow spatially, temporally, and socially. Crampton et al., for example, followed "#LexingtonPoliceScanner" to find out how riots spread online in the US. They suggest that researchers go beyond the geotag and focus on the space associated with the geolocation and not just the point on the map, but it should be borne in mind that they were focusing on a localized event in one fixed location. We argue against this practice, as we have found that the geolocation, which for us is the most important aspect, is often omitted in secondary research analyses.
Key words that link "sports" and "Twitter" on web search engines, at least in the English language, typically identify research focusing more broadly on sports journalism, and on finding sports events. These results are linked to how the art of journalism has had to adapt to reporting news in different ways (Schultz and Sheffer,), for example, or how social media can be used alongside humans as real-time sensors to find out when sporting events are taking place (Lanagan and Smeaton,; Zhao et al.,). Smith et al. point out that sports fans enhance their live sports viewing by using Twitter. This is a sentiment that has been noted in other studies, not only among fans but also among coaches, athletes, and sports media associates, originating in particular at the London Olympics in 2012, which was known as the "first social media Olympics" (Mann,). In summary, the kind of volunteered geographic information mentioned above has long been used on other social-media platforms such as Flickr photos and Google Maps placemarks, which Crampton et al. call the "geographies of the geoweb."
However, what is missing from these examples is the vital aspect of our research, namely where these tweets about sporting and news events are produced (Gritta et al.,), especially those in non-fixed locations. A similar result would be found in data from mobile network infrastructures, called transactional data, which Raun et al. cite has the potential to reveal activity spaces for second home usage, but still with a focus on the "where" and "when" of fixed locations. Although some sporting events are obvious, this is not the case with less widely known or news events, or informal leisure sports. The "where" of an event should be attached to a specific and unique location, and this spatial aspect (geolocation) is available as a geotag on Twitter (Middleton et al.,). We are aware that users post about and interact with sporting events, and we wonder if people in general also tweet about their own physical activities. Then "when" is not so important in our case, given that many previous studies have focused on this, such as Zhao et al. as well as Lanagan and Smeaton.
Previous geotagged Twitter tweet studies have begun to uncover land use functions including sport-related urban land use, such as Iranmanesh et al., but they do not mention which sporting activities and still omit the land cover type that the activity is occurring on. There should hence be more emphasis on the more specific "where," which yields information for our study about which urban PA locations are popular in terms of user demand, and could help municipalities to keep up their maintenance or improve the usability of locations in the HMA. We are aware that the City of Helsinki already uses some people counters in specific outdoor PA spaces (Ramo,), but although this example includes outdoor gym demand, it omits all other types of PA that might go on in the HMA. Members of the public have also noted that the maintenance of outdoor gyms could be improved, and that this could correlate directly with user demand. Therefore, Twitter messages would be a more well-rounded data source of skiing tweets among a wider population, as well as of other sports-related key words in the same locations.