Parameters for Designing Functional and Quality Pocket Open Spaces in High-Density Cities

Abstract

This study discusses parameters that are important for designing quality and functional open spaces in high-density cities. Research is often limited to large parks and public squares; studies on open spaces in high-density cities are rare. Hong Kong is a high-density high-rise city where people live in compact living environments small as 12 sqm. In such contexts, open spaces play a pivotal role on human well-being. Hong Kong consists of many pocket open spaces that are intended for passive recreation. Elderly use these public amenities predominantly. Therefore, accessibility, safety and user comfort become significant considerations. Improving existing pocket open spaces is essential since there are no plans for new parks in old districts. This study analysed eight pocket open spaces, adopting for their qualitative attributes. Microclimatic field data, photographic analysis, shadow analysis simulation and user perception survey shed light on spatial design, comfort and functional aspects. This study contributed to knowledge by developing guidelines to promote quality and functionality of pocket open spaces in high-density cities.

1. Introduction

This study adopted qualitative attributes of quality open spaces from [1, 2, 3] for analysing pocket open spaces. Research related to parks is often limited to large parks and public squares. Studies on pocket open space in high-density cities are rare. Most pocket open spaces in Hong Kong are smaller than 1000 sqm falling short compared with open space provision in other metropolitan cities. Hong Kong is a high-density high-rise city with urban population density exceeding 7126 per sqkm. Only 25% land area is developed due to challenging terrain conditions. There is a significant need for urban parks for improving emotional and physical well-being of residents who live in compact living environments as small as 12 sqm in high-rise buildings.

Zoning plans prescribe total percentage of open spaces per district based on population without further guidelines on location, size, required amenities, spatial quality and landscape design. Residual spaces in districts that were developed in 1970s were later transformed into public open spaces. Pocket open spaces considered for this study are district and local-level public amenities intended for passive recreation for the surrounding community. These are primarily being used by elderly daily in the community.

1.1 Case study district

A mixed-use residential and commercial district built under the ‘new town development programme’ in early 1970s provided the context for this study. This 6000 ha district accommodates 302,814 inhabitants with a density of 5300 persons per sq.km and a stock of 103,219 households. About 21.5% population are above 60 years of age [4]. To facilitate emotional and physical well-being of the increasing ageing population, easily accessible and safe outdoor amenities are vital. Although open space per capita 1 sqm in Hong Kong is far below compared with many other metropolitan cities, 87% residents live within 400 m and 94% within 800 m to public open spaces in this district [5]. In total, 131.84 ha are zoned as open spaces with sizes ranging from > 1 ha to 5 ha< to provide active and passive recreational facilities for the community [6]. Six out of eight pocket open spaces considered for this study are less than 1 ha. However, the total district-level open space provision is almost twice compared with recommended 20 ha for a population of 100,000 by the guidelines.

Average wind speed in most urban areas is approximately 1 m/s. Humidity levels from June to September range between 75 and 84% with average summer temperature reaching 34.5°C [7]. High humidity, hot weather, low wind velocity and poor air quality are key challenges deterring the enjoyment of outdoor life. Although predominant summer wind directions in this district are from the East, South and South-East quarters [8], street grids are aligned to South-East and North-West directions without facilitating adequate wind flow along the streets. Longer span of 90% of these pocket open spaces is aligned to North-East and South-West direction.

2. Influence of external parameters on open spaces

This section establishes criteria important for designing quality and functional open spaces based on previous research, benchmarking standards and guidelines. Gehl and Svarre [1, 2, 3] have contributed to the knowledge immensely through their comprehensive research on public spaces. Twelve quality criteria by Gehl Institute [3] emphasize on human perception and experience-associated aspects such as protection, comfort and enjoyment linked to public spaces. Scholars defined spatial and functional attributes of open spaces; as unbuilt spaces with a high proportion of natural elements [9, 10] cultural landscapes for socializing [11], spaces for human health, well-being and social cohesion [12] and areas for neighbourhood recreation [13]. This research extends Gehl’s matrix [3] by incorporating spatial design, microclimatic and functional dimensions and responses from the surrounding built environment.

2.1 Role of open spaces on human well-being

Undeniably open spaces contribute to human well-being and quality of life besides creating desirable microclimates. World Health Organization [12] advocates open spaces for promoting healthy, liveable and sustainable cities. Green open spaces contribute to the sustainability of compact cities [14]. Dines et al. [15] opine that ‘for most people, every day public spaces provide opportunities both as places of interaction and as places of retreat’. Scholars correlate nature connectedness with improved emotional and physical well-being [16, 17] and quality of life [18]. Pivotal attributes for creating quality and functional open spaces are proximity to where people live or work [19, 20, 21], presence of natural features [21, 22], cleanliness and maintenance [21], presence of amenities [22], sufficient park size [20] and people’s participation in planning green spaces [23]. Summarizing [14] claims strategic planning, design and management as the key criteria for delivering functionality and benefits.

2.2 User comfort parameters

Environmental parameters such as air temperature, mean radiant temperature, wind speed and relative humidity surrounding open spaces affect thermal comfort in addition to personal parameters such as clothing insulation and metabolic rate. High-density cities often suffer from low levels of urban ventilation, yet significant level of shading from the surrounding built environment. Scholars disagree with the use of thermal comfort as feedback for design decisions due to subjective preferences by individuals and the absence of suitable thermal comfort indices for specific outdoor conditions [24, 25, 26]. Given the subjectivity of thermal comfort perception, Jansson [14] and Jendritzky et al. [27] recommend reliance on meteorological variables as a reasonable way of inferring thermal comfort conditions. Confirming this approach, Rose et al. [28] argues the importance of understanding influence from key environmental factors affecting outdoor thermal comfort, but the futility of design interventions to modify outdoor thermal comfort conditions.

2.3 Influence of greenery and hardscape on microclimatic conditions

Most urban areas consist of increased amount of impervious material that aggravates Urban Heat Island (UHI) effect through increased air temperature. Scholars advocate the use of high-albedo material for mitigating UHI effect [29, 30, 31]. Cool paving materials have shown promising results in lowering surface temperature due to their high solar reflectance and low heat storage properties [30, 32]. Although cool paving reduces air temperature, a study by Erell et al. [33] suggests their inadequacy in reducing radiant heat. Shading helps reduce mean radiant temperature compared with exposed open areas. Studies from Singapore, Taiwan and Tokyo that represent similar urban morphological and climatological conditions to Hong Kong report correlations between greenery and air temperature. Chau et al. [34] reports 1.3°C temperature difference between areas with greenery and their surroundings in Hong Kong urban parks. He further reported 1–2°C lower temperature inside the parks compared with 150 m away from the parks. Similar findings were reported by Nichol [35] based on a study conducted in Singapore. Using a numerical model, Honjo and Takakura [36] established 300 m as the optimum influenced distance from a 100 m diameter green area. Supporting above recommendations, Chen and Wong [37] reported positive contributions from greenery on microclimates within and surrounding two large urban parks in Singapore.

Kawashima [38] compared surface temperature on vegetation, buildings and exposed soil based on satellite imagery confirming lowest surface temperature on vegetation (1.4–2.7°C) compared with buildings (2–3.4°C) and soil (2.3–4.9°C). Santamouris et al. [30] reported similar trends on tree canopies 32.9°C, grass 35.6°C, under tree canopies 28.7°C and exposed concrete areas 40.7°C in Singapore CBD. Even small green areas such as 40 × 60 m have shown 3°C reduction in temperatures in summer compared with outside areas [39]. These studies have established the role of greenery in lowering surface temperature and air temperature cooling the surrounding environment through shading and evapotranspiration.

Due to extreme high density in Hong Kong, impacts from building envelope albedo could be serious. Besides building masses, majority of horizontal surfaces are predominantly paved with very little soft landscape. Studies that compared thermal properties argued that grass and poly material contribute to very low amount of thermal energy, thereby reducing UHI effect compared with concrete and asphalt [40, 41, 42]. A study in Tokyo reported 2°C lower surface temperature at 1.2 m above grass compared with asphalt and concrete surfaces [43]. Similar conclusions were arrived at a study that compared grass and asphalt in Iran [37]. These studies support the role of urban greening on reducing air and mean radiant temperature through evapotranspiration in grass and reducing adverse impacts from low-albedo material such as asphalt.

2.4 Influence of sky view factor (SVF) on microclimatic conditions

Less sky exposure is attributed to less solar radiation entering the urban canyon, thereby reducing mean radiant temperature [44]. A study in Taipei city reported elevated temperature due to solar radiation absorption by unshaded hardscape areas within parks and surrounding areas [45]. The same study recommended reducing unshaded paved areas to less than 50% and to integrate at least 30% greenery and shading to alleviate negative effects. Comparison of three different shading scenarios; 4.9–9 m tall trees, pergolas at 4 m height around buildings with and without vegetation reported lowest mean radiant temperature around pergolas with vegetation [46]. Authors opine that pergolas and vegetation block longwave radiation. Ojaghlou and Khakzand [47] and Baghaeipoor and Nasrollahi [48] associated reduction in sky view factor (SVF) with reduction in mean radiant temperature. Analysing 18 600 × 600 m test sites in Hong Kong, Yuan and Chen [49] established a positive correlation between SVF and the Urban Heat Island effect. Adopting a software-based method [50] concluded a strong relationship between SVF and the temperature using areal means on a large sample area.

2.5 Qualitative parameters—Gehl’s 12 quality criteria for public spaces

Gehl’s 12 quality criteria combine human perception-based aspects such as protection, comfort and enjoyment articulated through pragmatic criteria (Table 1). Pragmatic aspects focus on accessibility, navigation within, seating options, safety concerns, impact from environmental conditions, aesthetics and how people interact. These criteria are derived from research on public spaces in European cities. Therefore, some of these criteria require modifications to suite high-density Hong Kong context.

Protection	Protection against traffic and accidents
	Protection against harm by others
	Protection against unpleasant sensory experience
Comfort	Options for mobility
	Options to stand and linger
	Option for sitting
	Options for seeing
	Options for talking/ hearing
	Options for play, exercise and activities
Enjoyment	Human scale
	Opportunities to enjoy positive aspects of climate
	Experience of aesthetic qualities and positive sensory experiences

Table 1.

Gehl’s 12 quality criteria (2018) for public urban spaces (source: adopted from Gehl and Svarre [3]).

2.6 Hong Kong Planning Standards and Guidelines (HKPSG)

Hong Kong Planning Standards and Guidelines [6] advocate sustainable and liveable open spaces through four guiding principles: ‘quantity’, ‘quality’, ‘good practice’ and ‘vision’ (Table 2). HKSAR Planning Department [6] recommends that open spaces should be safe, functional, accessible and usable spaces for the community, not just residual spaces for merely fulfilling regulations. Local open spaces are non-statutory land uses and should be at least 500 sqm in extent in urban areas intended for passive uses. Government Greening Policy aspires enhancing urban ecology by active planting and preserving and maintaining trees.

Quantity	1 sqm per person for district level and local level open spaces
Quality	high quality facilities, environmental standards and layout design in-line with users’ aspirations
Good practice	provide easy access, improve facilities as a community
Vision	assessment of existing facilities in relation to location, demographics, land uses and functions and socio-economic characteristics and prospects for future developments of the district

Table 2.

HKPSG on delivering sustainable and liveable open spaces.

Open spaces should cater to elderly, persons with disability, children and adults in an integrated manner; therefore, safety is a major consideration in open space design with regard to location, identifiable entrances, surface texture and facilities provided. Provision of slip resistant surface finishes, adequate furniture and positioning them under shading and away from the pedestrian paths are essential.

However, these guidelines do not provide measurable criteria for designing or assessing open spaces in relation to quality, good practices and vision objectives in Table 2.

3. Developing spatial design and user comfort parameters for functional pocket open space design

3.1 Scale, accessibility and safety

Since the case study district was developed prior to the announcement of HKPSG [6], most open spaces considered for this study do not adhere to the guidelines. In total, 500 sqm minimum open space extent and 1 sqm per capita requirements have not been met in most instances. Majority of pocket open spaces appears to be residual spaces located amidst of commercial areas, residential blocks and adjacent to traffic roads.

Open spaces in the case study district varied from 200 sqm to 10,600 sqm, with only four out of eight open spaces being over 500 sqm. All eight urban public open spaces are located within 100 m radius from residential and commercial neighbourhoods and are well integrated into the urban fabric ensuring safety and easy accessibility (Figure 1). ‘LEED Cities and Communities Plan and Design Standards’ [51] specify 11.25 sqm per capita green open spaces within 400 m radius from residential areas.

Figure 1.

Park network indicating location and orientation in relation to summer wind directions; East, South and South-East quarters.

Surrounding context consists of six to seven storeys tall old Chinese shop houses and 10–15 storeys tall public housing estates providing sense of human scale and sense of protection. Given the long operating hours of the commercial areas until 10 pm, these parks are well lit during day and night. Survey respondents appreciated the proximity, sense of safety, emotional comfort and physical well-being they receive by these pocket open spaces. Mantler and Logan [16] and McEwan et al. [18] reported positive impacts on adults spending time outdoors. Two open spaces are located adjacent to major traffic roads curtailing the enjoyment due to likely traffic accidents, exposure to noise and air pollution. These parks are completely pedestrianized; therefore, no bicycle paths are provided.

Analysing large number of open spaces in Hong Kong, Civic Exchange Hong Kong [52] opines, ‘access and linkages’, ‘comfort and image’, ‘uses and activities’ and ‘sociability’ are vital in creating quality open spaces. Overall, these parks aligned with over 60% of the ‘protection’ and ‘comfort’ criteria according to Gehl’s matrix.

3.2 Spatial design and quality

User survey and field studies revealed that these open spaces are primarily being used for passive recreation by senior citizens during late mornings and late afternoons. All these pocket open spaces are accessible to elderly and disabled persons. One consists of basic fitness equipment for elderly, and two consist of play elements for children. Six out of eight open spaces are predominantly made of hardscape. HKSAR Planning Department [6] stipulates minimum 70% soft landscape inclusive of 60% trees for passive recreational areas. None of these open spaces have achieved these standards as these parks were established before the guidelines were enacted. Although they are conveniently located, there are no identifiable entrances or boundaries to majority of these open spaces. Due to the compact size, navigation within was straightforward, however, lacked clear demarcations between sitting-out areas and pedestrian paths. Only the largest park is designed with defined landscape and hardscape areas, walkways and variety of sitting-out areas for small and large groups. Although seating has been the primary attraction in these open spaces, current seating arrangement is ad hoc; not all seating places are provided in shaded areas. Photographic survey confirmed users’ preference for shaded areas.

Although seating has been the primary attraction in these pocket open spaces, shadow analysis confirmed random positioning of seating without aligning with shading that occurs from the surrounding built environment. Five open spaces are paved with light colour cement blocks; two with orange colour eco blocks and two open spaces surfaced with dark colour rubber mats in the activity areas. None of these open spaces have paid attention to views or focal points.

These open spaces demonstrated about 50% alignment with the ‘comfort/ spatial design and quality’ criteria in the matrix.

3.3 Microclimatic aspects and user comfort

Air temperature, solar radiation, relative humidity, wind speed and direction were considered as the meteorological measurements affecting thermal comfort.

Urban heat island effect caused by excessive hardscapes in the parks and surrounding building density and low urban wind speed challenge user comfort during summer. Figure 2 presents an analysis of hardscape to greenery ratio and orientation in relation to summer wind directions; East, South and South-East quarters.

Figure 2.

Microclimatic and spatial analysis of the pocket parks.

Figure 3 presents a strong inverse correlation between greenery percentage and air temperature with r= −0.77 supporting that increased vegetation helps reduce air temperature in these pocket open spaces. Although the temperature range was narrow, lowest temperature values are associated with greenery above 49%. Effectiveness of trees in lowering air temperature in parks and the vicinity have been reported by previous scholars [29, 30, 31, 32].

Figure 3.

Correlation between air temperature and greenery % in pocket open spaces.

Santillán-Soto et al. [40] reported elevated temperature levels in unshaded hardscapes in parks in Taipei due to solar radiation absorption. This study recommended that parks should be designed with less than 50% of paved areas and at least 30% of vegetation and shading. On the contrary to scholars’ definition of open spaces as unbuilt spatial and functional features with high proportion of natural elements [9] and areas with permeable soft surfaces [53], seven out of eight pocket open spaces predominantly consisted of hardscape despite prevalent 2–3.5°C UHI effect in Hong Kong [54]. BEAM Plus Hong Kong green building guidelines recommend 50% or more passive open spaces and pedestrian zones to achieve thermal comfort [55]. Although these standards refer to new development projects, they provide a quantifiable criterion applicable to Hong Kong.

Figure 4 indicates a strong inverse correlation with r= −0.86; parks with higher greenery percentages reported lower wind speeds perhaps due to friction created by hedges and shrubs. Refs. [56, 57, 58, 59] also confirmed reduced wind speed within urban canopy due to trees. Parks with open passages diagonal or perpendicular to the prevailing wind directions reported high wind speeds.

Figure 4.

Greenery % and wind speed in pocket open spaces.

Hong Kong experiences a warm humid summer with high relative humidity and low wind speed affecting outdoor thermal comfort. In Hong Kong at 28°C temperature, a wind speed of 0.9–1.3 m/s is required to provide neutral thermal comfort for a person in light clothing [60]. All open spaces reported above 28°C, yet with wind speeds ranging between 0.9 and 1.8 m/s presumably providing users with comfortable outdoor thermal environments.

These open spaces are surrounded by mid-rise to high-rise buildings, casting partial shadows at different times during the day (Figure 5). Number of scholars have associated low Sky View Factor (SVF) with low air temperature due to reduced solar radiation [39, 42, 43, 44, 45]. This is another indication of desirable thermal comfort in these parks if seating positions are aligned with these shadow patterns. These open spaces demonstrated about 60% alignment with ‘enjoyment/ microclimatic and thermal comfort aspects’ in Gehl’s quality criteria matrix [3].

Figure 5.

Shadow analysis that compares 11:30 and 15:30 h on a sunny day.

3.4 User perceptions and expectations

Findings and guidelines from [3, 5, 6, 47] were adopted when developing user survey. Purpose of the survey was to understand users’ perceptions associated with these pocket open spaces and to understand their expectations. Most frequent users are male over 50 who use these pocket open spaces 5–7 days a week: whilst users between 30 and 40 years old use them less than 2 days a week between 3 and 6 pm. All age groups use these parks for relaxation and socializing with friends.

Users appreciate the proximity of these open spaces to their neighbourhoods and the use of slip resistant paving material providing them sense of safety, emotional comfort and physical well-being. World Health Organization [12] emphasizes the need for green spaces and their proximity; refs. [16, 18] confirm positive impacts on adults spending time outdoors.

Users’ concerns include small size, over crowdedness, noise, lack of separation from traffic roads, with further emphasis on the need for improving functionality, quality and comfort-related aspects such as pavilions for resting, seating under shade, sanitary facilities, hygiene and more landscape. Further they wish for large parks, large canopy trees, colourful landscapes, natural elements and views.

4. Recommended criteria for creating quality and functional pocket open spaces

Considering the increasing ageing population in Hong Kong, public amenities should adopt an all-encompassing approach to ensure user comfort, well-being and safety. Key parameters are categorized into the following: planning, spatial and design, landscape, facilities, maintenance. Current planning regulations should focus on specifying strategic locations for positioning open spaces besides providing guidelines. Table 3 presents recommendations.

	Aspect	Current provision	Recommendation and [relevant references]
Planning aspects	Location	Randomly located	Provide open spaces away from major traffic roads, yet in close proximity to neighbourhoods [3] Define specific locations on district Outline Zoning Plans. Demarcate clear boundaries and recognizable entrances
	Accessibility	No radius specified other than easy access [6]	Within 400 m radius [51]
Spatial and design aspects	Provision	1 sqm per capita	Minimum 4 sqm per capita [52] Combine scattered and small open spaces to form large parks at least 5000 sqm [6]
	Configuration	Ill-defined	Regular and defined space [61] Well-proportioned [61]
	Universal accessibility	All parks are elderly friendly	Avoid steps [62] Adopt ramps not less than 1:12 gradient with guardrails, and tactile paving for elderly and disables [62]
	Surface material	Hardscape	Soft anti-skid material and tactile paving [62] Introduce colours to increase contrast for elderly [62] Use permeable material or grass cover to prevent storm water stagnation Use high-albedo material to reduce Urban Heat Island effect Reduce concrete paving [3, 63] Adopt combination of vegetation ground cover and cool paving or high-albedo material to reduce radiant temperature [30, 32, 33, 38, 39, 42]
	Landscape	Not according to any guidelines	Increase vegetation ground cover to reduce air temperature [38, 39, 42] 70% landscape with 60% trees [6] Large tall trees for shading and to prevent obstruction to wind paths [56, 57, 58, 59, 64] Colourful flowering plants [based on user survey] Ecological continuity with native plants for low maintenance [61]
	Seating arrangement	Randomly located and on exposed areas	Variety of seating for small and large groups under shading [3] Seating provided under shading Seating away from pedestrian paths [based on user survey and shadow analysis]
Comfort	Lighting	Well-lit during daytime Street / park lighting and lighting from surrounding environment at night	Sensor driven lighting to provide protection and for energy efficiency Downward lighting to prevent nightlight pollution
	Thermal comfort	Low wind speeds Unshaded areas Heat absorbing hard surfaces	Pavilions and trees for shading [34, 35, 36, 37] Provide wind deflectors to divert S, SE, E wind to these parks Refer to hardscape and landscape recommendations above
	Noise and pollution mitigation	Some parks are bordering traffic roads	Avoid parks adjacent to traffic roads For existing parks install noise barriers adjacent to traffic roads Plant trees to reduce pollutants [64, 65, 66, 67]
	Well-being	No attention to well-being aspects	Create views (sculptures, arts, mural, fountains etc. to increase aesthetic appeal) Integrate natural elements such as stones, wood, water, trees Create variety of different zones within to cater to personal preferences based on user survey and [68]
	Facilities	Not provided on a consistent basis	Drinking fountains [68], toilets Fitness equipment Play equipment [based on user survey]
Operational & feedback	Maintenance Feedback	Managed by Leisure and Cultural Services Department (LCSD)	Involve community in maintaining these open spaces Require regular maintenance and guidelines for users Conduct community engagement exercises when planning and upgrading open spaces [69, 70]

Table 3.

Recommended planning, spatial, comfort and operational criteria for creating functional and quality pocket open spaces.

5. Limitations and further research directions

This study revealed number of correlations that are worthy of further investigations. Impacts from shading by surrounding buildings on reducing air temperature are pertinent and beneficial to high-density cities. Although trees contribute to reducing air temperature, further studies are important to establishing tree densities or layouts that would not compromise wind speed within the urban canopy.

6. Conclusions

This study focused on the functionality and quality of public pocket open spaces in extremely high-density Hong Kong where people live in compact high-rise towers. Eight open spaces from a mixed-use residential district that was developed in early 1970s provided the context for this study. Over 21.5% of population represents elderly above 60 years. All these open spaces have followed inclusive design principles making them elderly- and disable-friendly.

This study adopted Planning Standards and Guidelines Draft Outline Zoning Plan 2017 four principles: ‘quantity’, ‘quality’, ‘vision’ and ‘good practice’, Gehl’s ‘twelve quality criteria for experiencing public spaces’ as the basis for qualitative analysis validated by spatial, microclimatic, shadow analysis, photographic data, user behaviour patterns and user perception surveys.

Certain aspects in Gehl quality criteria [3] were not applicable to Hong Kong context. This study contributed to knowledge by developing design guidelines to promote quality and functionality of pocket open spaces in high-density cities. In terms of open space per capita and the extent, these pocket open spaces fell short compared with other similar cities in Asia [47]. Proximity of these open spaces to residential estates and commercial developments contributed to sense of protection, accessibility and frequent usage by the elderly in the late afternoons when parks cool off.

Given the small scale, navigation within was convenient. These parks had no clear entrances and segregation between pedestrian paths and seating areas. Seating areas are randomly positioned without benefiting from shading that occurs from the surrounding tall buildings.

Majority of these parks predominantly consisted of hardscape despite prevalent urban heat island effect. However, field data supported desirable thermal comfort conditions in these parks perhaps attributed to combination of other factors such as shading from surrounding buildings, alignment to wind paths and vegetation in some parks.

Landscape, shading, seating arrangements and provision of sanitary facilities require improvement to promote user comfort and well-being. User survey confirmed findings from qualitative, spatial and microclimatic analysis.

Although these parks made no reference to any standards at the time they were developed, majority of the parks indicated considerable alignment with Gehl’s quality criteria.

Acknowledgments

The author is grateful to Chu Hai College of Higher Education for research funding. Author would like to thank student assistants, Lam Ho and Yiksun Lai, for their contribution in data collection, graphics and simulation studies, Dyrus Hau, Joyce Lee, Joanna Chan and Villy Choi for conducting user surveys and Mr. R. Tan for sharing planning guidelines knowledge.

Conflict of interest

The authors declare no conflict of interest.