In selecting sites to survey it is important to have an unbiased method of selection. The survey teams are not allowed judgment in the field in selecting sites, but rather this is done using a pre-selection technique. In this way, neither the "dirtiest" nor the "cleanest" locations are picked. The survey teams count litter at sites that are selected well in advance of traveling to the location.
To select sites for a given jurisdiction a geographical information system (GIS) database is acquired (software used was ArcView GIS 3.2 by Environmental Systems Research Institute Inc.). Using the program, centre-line coordinates for all potential public street locations within the jurisdiction is selected.
Then using a random number generator feature of a spreadsheet program (Microsoft Excel) samples of this data are assembled. The data locations outputted centre-line locations for a statistically significant sample of potential sites.
Once the potential sample sites are re-plotted as a GIS map, for the entire survey area, detailed street or highway maps are used to accurately locate the sites, and to allow the writing of directions to the site by survey teams.
FIGURE 1 - MAP - RANDOM SITE MAP
Sites are rejected if they are located:
- on major highways / freeways
- location was on a bridge
- location clearly within a construction area
- on railway / subway right-of-ways
- on hydroelectric power line right-of-ways
- on / within water (ponds, rivers, streams/ lakes)
- access was difficult or impossible
- if located on industrial or private lands
Using a site description form, each site has directions written for a field team to locate and travel to the site. The directions were written in a manner that would allow any field team to find the site easily. Field teams travel to the sites using these directions so that no bias towards whether the site was dirty or clean would be introduced.