This article focuses specifically on the\u00a0second challenge highlighted by runoff studies, i.e. clarifying the\u00a0boundary between settlements and the\u00a0surrounding landscape from the\u00a0perspective of the\u00a0hydrological regime and potential adaptation to climate change. Approaches to managing rainfall, as well as the\u00a0risks and options for adaptation measures associated with extreme precipitation, differ between open countryside and settlements. The\u00a0boundary between them is not sharply defined and depends, among other factors, on the\u00a0size and fragmentation of urban areas. This paper describes the\u00a0delineation of only Hydrologically significant urban areas<\/em>; however, for the\u00a0sake of readability, the\u00a0shortened term Urban areas, or its abbreviation UA, will be used in the\u00a0following text. The\u00a0delineation of their boundaries utilised detailed and openly accessible national data\u00a0from the\u00a0Basic Geographic Data\u00a0Database of the\u00a0Czech Republic (ZABAGED\u00ae)\u00a0[3], supported by additional specialised data\u00a0sources (Digital Technical Map, Register of Territorial Identification, Addresses and Real Estate, etc.). This article presents, in limited detail, the\u00a0procedures used to define the\u00a0boundaries of UA, which were created as auxiliary outputs within the\u00a0framework of the\u00a0TA\u00a0CR project no. SS06010386 \u201cAdaptation of Urban Areas to Flash Floods and Drought<\/em>\u201d. Parts of the\u00a0text are based on the\u00a0interim report on the\u00a0project\u2019s\u00a0progress for 2024\u00a0[4].<\/p>\n Before spatially delineating the boundaries of an urban area, it is first necessary to define it as precisely as possible. Despite the common use (in Czech, translator\u2019s note) of the term \u2018intravil\u00e1n\u2019 (of settlements), it is not a terminologically\u00a0well-defined concept. It also does not translate well into English\u00a0\u2013 it is simply \u2018built-up area\u2019 or \u2018inner urban\u2019. There are differences between the\u00a0property-law perspective and the\u00a0spatial planning or urbanistic perspective. From a\u00a0legal standpoint (Act No. 128\/2000 Coll., on municipalities), intravil\u00e1n is defined as the\u00a0built-up area\u00a0of a\u00a0municipality that was recorded as intravil\u00e1n in the\u00a0cadastral map as of 1 September 1966. This is a\u00a0historical legal term, primarily relevant in connection with soil fund protection. Both older and current building legislation (Act No. 183\/2006 Coll. and Act No. 283\/2021 Coll.) no longer use this term directly; instead, they operate with the\u00a0concepts of built-up area\u00a0(zastav\u011bn\u00e9 \u00fazem\u00ed; Z\u00da) and developable area\u00a0(zastaviteln\u00e9 plochy; ZP), which are delineated in the\u00a0spatial plan. According to the\u00a0wording of \u00a7\u202f116 of Act No. 283\/2021 Coll., the\u00a0built-up area\u00a0(Z\u00da) includes:<\/p>\n From an urban planning and spatial development perspective, the\u00a0built-up area\u00a0is understood as the\u00a0compact part of a\u00a0municipality or town where built-up functions predominate (residential, commercial, industrial). Considering possible spatial arrangements, settlements can be distinguished as compact (the\u00a0main contiguous built-up area\u00a0of the\u00a0municipality), dispersed settlements, and isolated homesteads. The\u00a0spatial delineation of urban areas itself is a\u00a0relatively complex and expert process within this field. For example, the\u00a0Methodology for the\u00a0Identification and Classification of Areas with Urban Values<\/em>\u00a0[5], which establishes an objective framework for identifying and classifying areas with urban values as one of the\u00a0phenomena\u00a0monitored for Territorial Analytical Documents, recommends the\u00a0use of a\u00a0combination of diverse cartographic materials and results from field surveys. The\u00a0precise delineation is left to expert assessment and analysis of the\u00a0character of the\u00a0specific area.<\/p>\n From both of the\u00a0above-mentioned approaches (property-law and urban), it is evident that delineating the\u00a0built-up area\u00a0is not an easy task, where individual classes of topographical features could simply be grouped without regard to other spatial relationships with their surroundings. The\u00a0definition of (hydrologically significant<\/em>) Urban areas<\/em> applied in the\u00a0aforementioned project no. SS06010386 is also based on a\u00a0combination of these approaches. It refers to spatially extensive compact areas consisting of contiguous zones with residential or commercial-industrial functions, along with smaller internal islands or plots of a\u00a0predominantly natural character. Areas of UA\u00a0defined in this way have, compared to the\u00a0surrounding Natural features<\/em> (NF), despite including a\u00a0certain proportion of anthropogenic areas, a\u00a0different management of stormwater, risks, and impacts of fluvial and pluvial floods, and employ different methods of mitigation. Threshold values and criteria\u00a0for classifying objects or their classes were established during the\u00a0development of the\u00a0methodology on a\u00a0test area\u00a0exceeding 2,300 km\u00b2, which included parts of the\u00a0capital city Prague, medium-sized and smaller towns, as well as dispersed village settlements. The\u00a0GIS analyses described below were further processed using the\u00a0ArcGIS Pro environment.<\/p>\n The\u00a0methodology for creating the\u00a0data\u00a0layer of urban areas was developed using positional data\u00a0from the\u00a0ZABAGED\u00ae database from spring 2024 concerning the\u00a0test area\u00a0and was applied to the\u00a0entire Czech Republic using the\u00a0updated content of the\u00a0same database from December 2024. After an initial analysis of the\u00a0spatial relationships between individual object classes (layers) and their attribute sets, a\u00a0gradual classification of the\u00a0positional data\u00a0layers or their individual objects into natural and urban areas was carried out, starting with the\u00a0most numerous and clearly natural features and progressing to less numerous and ambiguously classifiable layers, including possible adjustments to the\u00a0geometry of certain objects. The\u00a0gradually expanded layer of natural features (NF) was used to classify objects of ambiguous classes, with one of the\u00a0main criteria\u00a0being the\u00a0ratio of each object\u2019s\u00a0shared boundary with this layer. At the\u00a0end of the\u00a0classification process, the\u00a0selected urban areas were aggregated into an initial approximate layer of urban areas (UA). In the\u00a0final phase, topological cleaning and filtering were performed based on the\u00a0size and significance of the\u00a0resulting UAs. In various parts of the\u00a0process, besides ZABAGED, selected classes of objects from the\u00a0Register of Territorial Identification, Addresses, and Real Estate (R\u00daIAN)\u00a0[7] and the\u00a0geometric delineations of land parcels recorded in the\u00a0Land Parcel Identification System (LPIS)\u00a0[6] were also used.<\/p>\n Classification of overlapping ZABAGED layers<\/strong><\/span><\/p>\n In the\u00a0Czech context, the\u00a0indispensable topographic database ZABAGED contains, in terms of spatial relationships, two types of polygon object classes: overlay and base (background). All base classes represent continuous areas with relatively homogeneous ground cover or type of use (e.g., permanent grassland, functional development) and together create a\u00a0topologically clean, continuous representation of the\u00a0entire territory of the\u00a0Czech Republic. In contrast, overlay classes most often represent man-made objects of various kinds (buildings, castles), but also natural features (swamps, peat bogs), which overlap with one or more base layers. In terms of their mutual positions, they are disjoint, but sharing a\u00a0common boundary is not excluded. Relevant overlay objects provide valuable information when deciding on the\u00a0classification of certain base layer objects into urban areas and defining their boundaries. Following an exploratory analysis, relevant classes were selected from the\u00a0overlay layers according to Tab.\u00a01<\/em>. All base layers were used to ensure the\u00a0integrity of the\u00a0derived UA\/NF polygons.<\/p>\n As is evident from their names in Tab.\u00a01<\/span><\/em>, even the\u00a0selected overlay object classes do not necessarily have the\u00a0same relevance when deciding whether to classify a\u00a0base layer object as part of a\u00a0significant urban area\u00a0or not. The\u00a0most problematic class is the\u00a0largest layer, Individual building<\/em> or Building block<\/em><\/span> (hereafter Buildings<\/span><\/em>), which includes an enormous number of objects of varying sizes and importance. The\u00a0attribute data\u00a0of this layer contributes only partially to their differentiation, as less than 2 % of nearly 3.9 million objects have a\u00a0defined specific building type from about 40 categories; the\u00a0remainder of the\u00a0objects are classified as Unspecified buildings<\/span><\/em>. Therefore, a\u00a0supplementary attribute called ZB_podklad<\/span>, named after the\u00a0base ZABAGED layer, was first assigned to these objects.<\/span><\/p>\n Because many of the\u00a0background layers (e.g. Functional development area<\/span><\/em>) include more detailed information on land use, which can play a\u00a0role in classification of Buildings<\/span><\/em>, this specific attribute was transferred to an additional field called ZB_detail<\/span>. Subsequently, Buildings<\/span><\/em> were classified according to these three attributes, and where applicable, by the\u00a0auxiliary criterion of their area, into three levels of significance (0\u20132) based on a\u00a0key, which is not detailed here due to its excessive length. In general terms, buildings of a\u00a0rather non-urban type (e.g. pumping stations, livestock farms, etc.) are initially marked as insignificant (significance = 0), while most of the\u00a0remaining specific types are assigned significance level 2. Furthermore, buildings that are unspecified but located on a\u00a0clearly non-urban background (such as forest land, solar power plant) are also marked as insignificant, with varying area\u00a0limits of 16\/500\/1,000 m\u00b2 applied in cases of ambiguous data. Specific combinations of characteristics were used for smaller buildings situated on the\u00a0Functional development area<\/span><\/em>\u00a0layer. Remaining unspecified buildings were assigned a\u00a0significance level of 1. In the\u00a0following phase, significance of Buildings<\/span><\/em> was taken into account when classifying objects in the\u00a0background layers; in some cases only significant Buildings<\/span><\/em> were considered, while in specific cases all Buildings<\/span><\/em> were used.<\/span><\/p>\n Sorting and adjustment of base ZABAGED layers<\/span><\/strong><\/p>\n All polygon object classes in ZABAGED\u00a0\u2013 both overlapping and background\u00a0\u2013 were analysed during the\u00a0exploratory phase in terms of the\u00a0existence, reliability, and relevance of their internal attributes. Careful classification of more than 60\u00a0categories of development types<\/span> required the\u00a0use of objects from the\u00a0Functional development area<\/span><\/em>\u00a0layer, which includes similar but not identical categories to the\u00a0building type<\/span> from the\u00a0overlapping Buildings<\/span><\/em> layer.<\/span><\/p>\n Objects from the\u00a0Arable land<\/span><\/em> layer and Other unspecified areas<\/em>\u00a0<\/span>\u2013 specifically one of its two categories, Other unspecified areas<\/em>\u00a0<\/span>\u2013 as well as the\u00a0layers Other area\u00a0in settlements<\/span><\/em> and Ornamental garden, park<\/span><\/em>, were found to be highly problematic and required advanced approaches when deriving urban areas (UA).<\/span><\/p>\n From the\u00a0linear object classes in ZABAGED, datasets related to transport infrastructure were used, specifically: Motorway<\/em>, Unregistered road<\/em>, Road under construction<\/em>, Street<\/em>, Railway line<\/em>,<\/span> and Railway siding<\/span><\/em>. In cases where a\u00a0Tunnel<\/span> object was found to run concurrently along the\u00a0route of any of these objects, the\u00a0covered sections were removed from the\u00a0dataset.<\/span><\/p>\n The\u00a0process of classifying and modifying individual ZABAGED background layers for subsequent compilation into the\u00a0final UA\/NF layer was tested and then automated using the\u00a0graphical programming environment ModelBuilder, combined with simple Python scripts within ArcGIS Pro. A\u00a0set of approximately 30\u00a0interconnected tools was created to support a\u00a0more transparent workflow and allow for intermediate product checks. Rather than directly aggregating objects that make up urban areas, the\u00a0proposed method focuses on the\u00a0inverse task\u00a0\u2013 identifying which objects represent typical natural features and, with a\u00a0high degree of certainty, do not belong to urban areas. Objects with ambiguous classification are then gradually analysed and sorted into either natural features (NF) or candidates for inclusion in UA, based on the\u00a0proportion of their shared boundary with a\u00a0NF. Geometric adjustments are made throughout to complex objects, and finally, all potential UA\u00a0objects are aggregated. Both working layers\u00a0\u2013 NF and UA\u00a0\u2013 are maintained in two variants throughout the\u00a0process: the\u00a0MERGE variant preserves internal object boundaries and retains the\u00a0relevant portion of their original attribute set, supplemented with a\u00a0source attribute indicating the\u00a0name of the\u00a0parent input layer. The\u00a0DISSOLVE variant consists only of merged polygons without internal boundaries, containing overall or average characteristics of the\u00a0area\u00a0(e.g. area\u00a0size, total surface area\u00a0and building footprint, shape index, etc.). A\u00a0brief description of the\u00a0processing of background layers follows below; a\u00a0detailed explanation exceeds the\u00a0scope of this article.<\/span><\/p>\n For analysis and adjustment of complex topographic classes, an auxiliary polygon grid of regular hexagons\u00a0\u2013 hexes\u00a0\u2013 was created at two scales. In the\u00a0base resolution, hexes were defined with an area\u00a0of 400 m\u00b2, corresponding to a\u00a0height of approximately 21 m. In the\u00a0lower-resolution version, the\u00a0hex height was set to 60\u00a0m. In both cases, the\u00a0hex grid covered the\u00a0entire territory of the\u00a0Czech Republic with a\u00a0slight overlap. To reduce computational demands, hexes located entirely within polygons of arable land and all forest land classes were removed, each reduced by an 80 m buffer. To support spatial analysis, hexes containing significant Buildings<\/span><\/em>, Castle<\/span><\/em>, or Covered structures<\/span><\/em> were then marked with attribute tags, as were their neighbouring hexes. Optionally, hexes containing all Buildings<\/span><\/em>, and those adjacent to them, were also marked.<\/span><\/p>\n In the\u00a0first step of processing the\u00a0base layers, adjustments were made to the\u00a0Other unspecified areas<\/em> (OUA)<\/span> within the\u00a0polygon layer Arable land<\/em> and other unspecified areas<\/em><\/span>. As shown in Fig.\u00a01<\/span><\/em>, OUA<\/span>\u00a0include both linear land objects such as roads in non-urban areas, along with adjacent greenery, and polygonal elements that may potentially contain buildings or other anthropogenic structures. These polygonal elements were automatically separated for potential later inclusion in the\u00a0UA\u00a0layer. First, uniform buffers around linear road objects were extracted from the\u00a0OUA<\/span>\u00a0objects, as well as any overlaps with the\u00a0LPIS layer. The\u00a0buffer widths listed in Tab.\u00a02<\/span><\/em> were determined for individual road classes based on a\u00a0review of technical standards, experience from previous projects, and random verification using aerial imagery. The\u00a0areas remaining after the\u00a0separation of road buffers were subsequently divided using the\u00a0basic hexagonal grid. For each fragment, the\u00a0relative position with respect to the\u00a0edge of the\u00a0original polygon, to the\u00a0road, and an indication of the\u00a0presence or proximity of Buildings<\/span><\/em> was determined. Fragments with a\u00a0suitably chosen combination of the\u00a0described attributes were re-aggregated into a\u00a0contiguous unit (see the\u00a0red-hatched object in Fig.\u00a01<\/span><\/em>), and the\u00a0total area\u00a0of included Buildings<\/span><\/em>, shape index, etc., were calculated. Finally, the\u00a0resulting polygons were filtered and classified\u00a0\u2013 based on experimentally determined parameter combinations\u00a0\u2013 into potential UA\u00a0elements and elements to be incorporated into the\u00a0NF layer.<\/span><\/p>\n <\/p>\n Before creating the\u00a0first iteration of the\u00a0NF layer, a\u00a0hypothesis was tested that, in the\u00a0case of compact development, buildings are always situated on a\u00a0typically urban-type base layer, such as Other settlement area<\/span><\/em>, Ornamental garden\/park<\/span><\/em>, Orchard\/garden<\/span><\/em>, etc. This assumption proved invalid in the\u00a0case of the\u00a0Permanent grassland<\/em> (TTP)<\/span> layer. Although this layer includes more or less maintained grassy areas in the\u00a0non-urban area, it also fills small gaps within settlements or even serves as the\u00a0base layer for relatively compactly arranged Buildings<\/span> <\/em>in settlements located in specific landscape types, such as mountain villages. An example of such a\u00a0settlement is shown in Fig.\u00a02<\/span><\/em>, where it is evident that a\u00a0blanket classification of TTP<\/span> as natural feature in these locations would lead to unacceptable fragmentation and the\u00a0subsequent exclusion of urban areas that in reality form a\u00a0fairly compact settlement centre. Therefore, significant segments of TTP<\/span> within a\u00a020 m buffer around Buildings<\/span><\/em> were excluded, with the\u00a0selection criteria\u00a0being an area\u00a0larger than 0.25 ha, the\u00a0presence of at least three buildings, and contact with or proximity to objects from the\u00a0layers Other settlement area<\/span><\/em>, areal features with buildings, and polygons of roads extracted from OUA<\/span>. The\u00a0remaining TTP<\/span> areas were then incorporated into the\u00a0first iteration of the\u00a0NF layer.<\/span><\/p>\n <\/p>\n In the\u00a0third step, the\u00a0first iteration of the\u00a0polygon layer for NF was created, incorporating either entire classes of objects or their subsets according to Tab.<\/span>\u00a03<\/span><\/em>. This was followed by a\u00a0rather complex processing of the\u00a0Ornamental parks and gardens<\/span><\/em> feature (hereinafter Parks<\/span><\/em>), which unfortunately lacks any relevant internal attributes and includes mainly urban residential greenery, but also larger maintained suburban green areas such as Pr\u016fhonice Park. These polygons often contain more or less significant buildings, both isolated and in groups, as well as numerous internal islands (especially around water bodies), which complicates spatial analyses and decisions regarding the\u00a0classification of the\u00a0object as part of either UA\u00a0or NF, as shown in Fig.<\/span>\u00a03<\/span><\/em>. First, polygons in Parks<\/span> <\/em>that are potentially natural (P_Park<\/span><\/em>) are separated if their shared boundary with NF accounts for at least two-thirds of their outer perimeter (excluding internal islands). This forms the\u00a0second iteration of the\u00a0NF layer. From the\u00a0potentially settlement-related Parks<\/span><\/em> (U_Park<\/span><\/em>), 75 m buffers around significant buildings and Castles<\/span> <\/em>are extracted. Due to frequent overlaps with neighbouring polygons, only those parts in direct contact with buildings or near Chateau<\/span><\/em> are isolated, while buffer areas forming isolated islands within the\u00a0original U_Park<\/span><\/em> are disregarded. Small fragments of U_Park<\/span><\/em> or fragments without contact with NF are reassigned back to the\u00a0subsets around Buildings<\/span><\/em>. For large fragments and those adjacent to PP, the\u00a0length of their outer perimeter (again excluding internal islands) and the\u00a0proportion of this perimeter shared with NF are calculated. Golf courses (a\u00a0category of the\u00a0Functional development area<\/span>\u00a0<\/em>layer) are temporarily included in the\u00a0NF set. The\u00a0shared perimeter is determined using a\u00a010 m buffer around NF to include cases where parks are separated from the\u00a0non-urban area\u00a0by only a\u00a0narrow road (most often represented by the\u00a0Other settlement<\/span> area<\/span><\/em>\u00a0base layer). Large fragments with less than 20 % shared perimeter with NF form the\u00a0final component that, together with the\u00a0building buffers, constitute the\u00a0resulting U_Park<\/span><\/em>. The\u00a0remaining objects, along with the\u00a0primarily designated P_Parks<\/span><\/em>, are assigned to the\u00a0NF layer, creating its third iteration.<\/span><\/p>\n After processing the\u00a0Parks<\/span><\/em>, the\u00a0objects from the\u00a0Orchard, garden<\/span><\/em> layer, specifically its Garden<\/span><\/em> category, were classified (the\u00a0remaining categories, Orchard<\/span><\/em> and Other permanent crops<\/span><\/em>, had already been included in NF in previous steps). From the\u00a0perspective of inclusion in UA, this category is also ambiguous, as it encompasses both family house plots within contiguous settlement areas and scattered complexes of suburban satellites, villages, or former allotment gardens whose function has gradually shifted to residential use (Fig.\u00a04<\/span><\/em>). Compared to Parks<\/span><\/em>, however, these objects are much simpler and more compact, which was reflected in the\u00a0classification approach applied to them. First, gardens not containing centroids of significant Buildings<\/span><\/em> (Gardens without buildings<\/span><\/em>) were isolated, and their objects with a\u00a0boundary shared with NF over two-thirds were assigned to the\u00a0fourth iteration of NF. Again, internal islands within the\u00a0polygons were disregarded. From the\u00a0remaining Gardens without buildings<\/span><\/em>, objects with no contact with any Building<\/span><\/em> polygons and with a\u00a0boundary shared with NF over 40 % were further removed and assigned to NF, resulting in the\u00a0fifth iteration of this layer. The\u00a0remaining Gardens without buildings<\/span><\/em>, as well as all gardens containing centroids of significant Buildings<\/span><\/em>, proceeded to further processing as potential UA\u00a0features.<\/span><\/p>\nMETHODOLOGY<\/h2>\n
Definition of the\u00a0built-up area\u00a0of a\u00a0settlement and\u00a0urban\u00a0areas<\/h3>\n
\n
Processing topographic objects and iteration of\u00a0the\u00a0natural features layer<\/h3>\n
Tab. 1. Selection of relevant ZABAGED overlay layers for sorting of the base layers<\/h5>\n
![\"\"](\"https:\/\/www.vtei.cz\/wp-content\/uploads\/2025\/08\/Strouhal-tab-1.jpg\")
<\/a>\nHexagonal grid for decomposition of complex objects<\/h3>\n
Tab. 2. Buffer widths for linear transport infrastructure according to type for purpose of\u00a0their separation from Other unspecified areas<\/h5>\n
<\/a>\nOther unspecified areas<\/h3>\n
<\/a>\nFig. 1. Other unspecified areas including both the areal feature of anthropogenized area (red hatch) and the pseudo-linear road parcel (grey) subject to automated separation<\/h6>\n
Permanent grassland<\/h3>\n
<\/a>\nFig. 2. Significant clipped areas of permanent grassland (deep yellow) for inclusion in\u00a0urbanized areas; light yellow is open grassland and shaded insignificant clipped areas with\u00a0scattered settlements<\/h6>\n
Tab. 3. Selection of base layers or their subsets for the first iteration of the Natural Feature layer
<\/a><\/h5>\nOrnamental parks and gardens<\/h3>\n
<\/a>\nFig. 3. Pr\u016fhonice park as the biggest challenge for processing and sorting Ornamental parks and gardens<\/em> (green objects with circles). A\u00a0typical natural feature, only sharing a\u00a0high percentage of perimeter with residential elements and containing a\u00a0number of isolated buildings and island objects; light green elements were included into the first version of Urban Areas<\/em> layer<\/h6>\n
Gardens<\/h3>\n