Wednesday, January 07, 2009
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TRANSECTS

6.1

What is a Transect?
6.1.1 A ‘transect’ is the name given to an area of relevant land or highway that is sampled as part of a NI 195 survey, and on which a grade is given for litter and another for detritus. There are broadly two types of transect: one on highway sites and the other on recreation and other open areas.
6.1.2 If a transect does not contain a metalled or paved surface a grade should not be given for detritus (a metalled surface is one that is made of broken stone that is mixed with asphalt to form tarmac).

6.2

Transects on Highways (Streets)
6.2.1 A transect on a highway is normally 50 metres long, extending the whole width of the street or highway from backline to backline. It will include footways, road channels, carriageways, pedestrian refuges, splitter islands, central reservations, and may also include landscaped areas such as verges, grassed areas, shrubbed areas, planters, tree pits and the bases of hedges and fences that bound areas of relevant land or highway.

6.2.1 Transect
6.2.2 On dual carriageways, or other roads which are judged to be too busy for surveyors to cross and re-cross safely, transects are selected which comprise 50 metre lengths of the highway from backline to centreline. Where this procedure is necessary, and more than one transect is being sampled from a particular highway, transects should be located alternately on opposite sides of the highway in order to take account of any uneven distributions of litter or detritus. The photograph illustrates the area that would be assessed in this case. Similarly, where the centreline of a road or street forms the boundary between two wards – the transect should comprise a 50 metre length of the highway from backline to centreline.

6.2.2
6.2.3 Different transects should be located at different places along the street – some next to road junctions, and others at different places along the length of the street. They should not all be located in the middle of the street.

6.3

Transects on Recreation Areas and other Open Spaces
6.3.1 No more than 5 transects should be surveyed on any one Recreation Area or open space.
6.3.2 Transects may take different forms in Recreation Areas and other open spaces. Along footways crossing such spaces, transects should normally be 50 metres long, and extend 2 metres onto grassed or other areas that lie either side of the path.
6.3.3 On larger open areas, such as sports fields and play areas, transects should not exceed 50 metres on either axis. This may mean subdividing the areas for survey purposes into a series of rectangular transects, which have maximum dimensions of 50 x 50 metres. Although in these cases, not all the transects will have the same dimensions.
6.3.4 The precise layout of the transects will be determined by the shape and functional characteristics of the open space in question. Figure 6.3.1 illustrates how different transects will be surveyed within Recreation Areas.
6.3.5 Try as far as possible to set the transects out in such a way that they encompass the different functional parts of recreation areas or open space. For example, in a park different transects should be arranged to cover features such as entrances, play areas, lakesides, car parks, footways, different types of landscaped areas, sports pitches (including where spectators congregate), bandstands etc.
6.3.6 The photographs in Figure 6.3.2 illustrate different examples of how transects could be selected for different recreational areas.

Fig. 6.3.1 Diagram of Transect Selection in Recreation Areas

6.3.1 Transect
 

6.3.2 Example Transects in Car Parks and Recreation Areas

6.3.2 
6.3.2 
6.3.2

6.4

How Many Transects should be Surveyed and When?
6.4.1 The NI 195 Survey for an authority should be based on three samples of 300 transects, each sample taken over a four-month period. The first sample should be obtained between April and July; the second from August to November; and the third from December to March of the following year. This ensures that the survey covers seasonal variations.
6.4.2 Each sample should contain a minimum of 30 transects in each ‘standard’ NI 195 Land Use Class (assuming that all ten NI 195 Land Use Classes are present in a district). More than 30 transects will be required to make up the overall target of 300 if not all of the ten land-uses are present (see below).

6.5

Why 300 Transects Overall, and 30 per Land-use?
6.5.1 The statistical reliability of NI 195 is linked to the size of the sample. This National Indicator needs to have an acceptable margin of error, particularly as it may be used in Local Area Agreements, and is likely to be reported by local authorities to a range of public and community bodies. This is the reason for requiring 300 transects in each four-month period and 900 over a full year.
6.5.2 Please see Section 15.5 for further information on the margins of error likely to be associated with estimates based on the NI 195 survey.
6.5.3 The minimum figure of 30 sites per land-use in each four-month period follows from dividing the 300 overall target between the ten standard land-uses. ENCAMS’ consultancy experience has shown that this size of sample, building up to 900 over a full year, is sufficient to provide indicative management information that is useful in reviewing and adjusting cleansing resource levels, priorities and strategies.

6.6

Transect Distribution
6.6.1 Surveyors should try to achieve a geographic ‘spread’ of transects across target wards, avoiding a situation where they are all clustered in a small part of the ward.
6.6.2 The example in the table in Section 6.7 does not relate to any actual authority, but shows some of the kinds of patterns that can result from following the rules set out in the section ‘How To Plan A Survey’.
6.6.3 This is an authority where there is only one area of Main Retail and Commercial Land Use, which lies outside the target wards for this survey. All 30 transects have been surveyed within this area, which will need to be surveyed (though with varying sets of transects, as far as possible) for each four-monthly NI 195 survey.
6.6.4 In brief, the table demonstrates the following:
  • Other Retail and Commercial centres are fairly widespread, but small, and the total has had to be ‘topped up’ with three transects outside the target wards.
  • High Obstruction Housing is represented in all the target wards, but there is only a very small amount in Ward 5.
  • Medium Obstruction Housing only occurs in three of the target wards.
  • Lower Obstruction Housing is absent from one of the target wards, so the total has been split as evenly as possible among the remaining four target wards.
  • Industry/Warehousing areas are only found in two of the wards, and the bulk of this type of land-use (18) has been found elsewhere in the authority.
  • Main Roads go through all the target wards.
  • Rural Roads only occur in three of the target wards, and in one of these only to a limited extent.
  • Other Highways are fairly widespread, but thin on the ground, and the balance (12) has had to be made up from other wards.
  • Recreation Areas are present and widespread through all the target wards.

6.7

Example Distribution of Transects Between Wards
 
Fig. 6.7.1: Example Distribution Of Transects Between Wards
  TARGET WARDS  
               
  WARD 1 WARD 2 WARD 3 WARD 4 WARD 5 OTHER WARDS TOTAL
               
LAND-USE              
               
Main Retail/Commercial 0 0 0 0 0 30 30
Other Retail/Commercial 3 9 4 6 5 3 30
High Obstruction Housing 7 7 7 7 2 0 30
Medium Obstruction Housing 10 0 0 10 10 0 30
Low Obstruction Housing 8 7 7 0 8 0 30
Industry/Warehousing/Retail Sheds 0 0 0 6 6 18 30
Main Roads 6 6 6 6 6 0 30
Rural Roads 12 0 0 13 5 0 30
Other Highways 4 4 3 4 2 12 30
Recreation Areas 6 6 6 6 6 0 30
               
TOTAL 56 39 33 58 50 63 300
6.7.1 Ideally, surveyors should aim to survey six transects in each land-use, in each of the five target wards. This would give 30 sites for each land-use, for the whole authority. Often, however, this is not possible.
6.7.2 In practice, for a particular four-monthly survey there may be situations where:
  • some land-uses may not be present in an authority;
  • there may be only very limited amounts of a particular land-use in an authority;
  • some land-uses may not be present in all of the target wards; or;
  • some land-uses may not be present in any of the target wards.
6.7.3 The basic principle is that as many transects as possible should be drawn from the target wards. However, where this is not possible, the following rules apply in the circumstances listed above.

6.8

Land Uses Not Present In An Authority
6.8.1 This situation is most common in the case of High Obstruction Housing (in rural areas); Low Obstruction Housing (in some parts of Inner London and, occasionally, other metropolitan areas); and Other Highways (in some authorities in London and other metropolitan areas).
6.8.2 Where one or more land-uses are not present in an authority, divide the target number of 300 sites equally between the remaining land-uses to determine the number of sample transects that need to be surveyed in each of the target wards. The resulting number should be rounded up to the next whole number, if necessary.
6.8.3 For example, if there is no High Obstruction Housing in an authority, divide the overall target of 300 by nine (the remaining number of Land Use Classes present). This would require 34 transects to be surveyed in each of the nine land-uses, giving a total of 306 transects. These 34 transects should then be divided as equally as possible between the five target wards. Six transects would be surveyed in one ward, and seven each in the remaining four wards.

For Example:

Number of Land Uses available Transects Per Land Use Transects Per Ward Total
10 30 6 300
9 34 6 in 1 and 7 in 4 306
8 38 7 in 2 and 8 in 3 304
7 43 8 in 2 and 9 in 3 301

6.9

Land Uses Not Present In An Authority
6.9.1 This situation can affect any of the three Housing Land Uses (High, Medium and Low Obstruction), and Other Highways, depending on the overall characteristics of an authority.
6.9.2 If 30 or more transects are present to be surveyed in a land-use throughout the district (even if it means surveying 100% of available sites on each 4-monthly survey), then that land-use should be included in the NI 195 return.
6.9.3 Where there is only a limited number of transects in a land use within an authority (but more than the minimum 30 needed for NI 195), surveyors should ‘rotate’ the transects so that they are all surveyed on a regular basis. They should not continue to survey the same transects in each four-monthly survey.
6.9.4 If less than 30 sites are available to be surveyed - even at 100% -then for the purposes of NI 195, the land-use should be treated as ‘not present’. However, the authority may wish to monitor conditions in that land-use, without including it in the NI 195 return.

6.10

Land Uses Not Present In An Authority
6.10.1 The most common kinds of situation are:
a. a land use is absent from one of the target wards (e.g. Low Obstruction Housing);
b. a land use is concentrated in one or two of the target wards (e.g. Main Retail and Commercial, or Industry/Warehousing/Retail Sheds);
c. a land use is thinly spread over parts of the District (e.g. Other Highways – urban alleyways, lay-bys and bridleways etc.).
6.10.2 Where it is not possible to achieve the target number of transects within the initial set of target wards, surveyors should go in the first instance to wards which are ‘adjacent’ on the list of wards ranked by the Index of Multiple Deprivation.
6.10.3 This is very likely to occur where land uses are only present to a limited extent within an authority (see Section 6.9).
6.10.4 If targets still cannot be met, surveyors should select transects in other wards, as close to the initial selection of target wards as possible in terms of deprivation.