Over 60 transects were walked in Hertfordshire and Middlesex in 2017
Transects are the main method of measuring how butterfly populations change with time. The technique is simple, involving walking the same set route every week in good weather throughout the summer months, and noting down the numbers of each species seen within about 5 metres. The method is described under BUTTERFLY TRANSECT MONITORING
Link sections on this page . . .
The transects walked in Hertfordshire and Middlesex since 2005 are listed here. Please note that some transects have not been walked continuously since 2005
| Name | Grid Ref | Last walked |
| Abney Park | TQ336868 | 2016 |
| Aldbury N1 | SP949138 | 2018 |
| Aldbury Nowers | SP952159 | 2018 |
| Balls Wood | TL344106 | 2018 |
| Bardon Clumps | TL318155 | 2017 |
| Batford Springs | TL145150 | 2018 |
| Beane Hill | TQ199873 | 2018 |
| Bedfont Lakes | TQ080724 | 2013 |
| Belmont Railway | TQ161897 | 2018 |
| Bencroft Field | TL330062 | 2018 |
| Bencroft Wood | TL335065 | 2018 |
| Birklands Meadow | TL168053 | 2005 |
| Bishops Stortford Southern Country Park | TL473193 | 2018 |
| Brent Reservoir | TQ213873 | 2012 |
| Bricket Wood Common | TL131009 | 2018 |
| Bronzefield | TQ055715 | 2010 |
| Broxbourne West Ride | TL325070 | 2018 |
| Bunkers Park | TL079058 | 2010 |
| Butterfly World | TL127043 | 2016 |
| Camley Street Natural Park | TQ299834 | 2017 |
| Clifford Road Allotments | TQ260967 | 2005 |
| Colney Heath Common | TL203057 | 2009 |
| Cranford Park South | TQ101779 | 2018 |
| Dane Farm Field, Kimpton | TL153173 | 2012 |
| Danemead Nature Reserve | TL346079 | 2018 |
| Danesbury Park | TL230170 | 2018 |
| Fir and Pond Woods | TL277006 | 2015 |
| Fryent Country Park | TQ195876 | 2018 |
| Gravel Hill | TL216170 | 2018 |
| Great Ashby | TL267269 | 2014 |
| Gunnersbury Triangle | TQ201786 | 2018 |
| Gutteridge Wood | TQ091843 | 2018 |
| Halsey Field | TL042088 | 2018 |
| Hampstead Heath | TQ270863 | 2018 |
| Harmondsworth Moor | TQ050775 | 2016 |
| Harpenden Common | TL137134 | 2018 |
| Heartwood Forest | TL163109 | 2018 |
| Heartwood Forest 2 | TL171123 | 2018 |
| Hedgeswood Common to Hoo Wood | TL031131 | 2018 |
| Horsenden Hill East | TQ162843 | 2018 |
| Horsenden Hill West | TQ163844 | 2018 |
| Hounslow Heath | TQ121749 | 2013 |
| Hunsdon Mead | TL416108 | 2009 |
| Kenwood | TQ271874 | 2014 |
| Kings Langley | TL068039 | 2010 |
| Knebworth | TL221208 | 2018 |
| Knebworth Woods | TL227227 | 2018 |
| Lake Farm Country Park | TQ090804 | 2018 |
| Lakeside NR | SP922124 | 2018 |
| Lee Valley Turnford | TL368043 | 2017 |
| Lemsford Springs | TL223121 | 2018 |
| London Zoo Car Park | TQ283836 | 2018 |
| London Zoo | TQ281834 | 2018 |
| Long Deans | TL073048 | 2005 |
| Mardley Heath | TL248184 | 2018 |
| Marshalls Heath | TL161149 | 2018 |
| Millhoppers | SP900149 | 2018 |
| Minet Country Park | TQ109802 | 2018 |
| Miswell Lane | SP914117 | 2018 |
| Nicky Line | TL116140 | 2005 |
| Northaw Great Wood | TL280040 | 2013 |
| Northaw Great Wood Bridleway | TL285043 | 2013 |
| Oughtonhead Common | TL169303 | 2009 |
| Panshanger Park - Arable field west | TL298129 | 2017 |
| Panshanger Park - Lady Hughes Wood | TL300125 | 2017 |
| Panshanger Park - Rifle Butts | TL299122 | 2017 |
| Parkland Walk South | TQ289879 | 2018 |
| Patmore Heath | TL442257 | 2018 |
| Perivale Wood | TQ159837 | 2018 |
| Pinn Meadow | TQ094880 | 2015 |
| Pishiobury Park | TL480135 | 2005 |
| Pryor's Wood | TL265265 | 2018 |
| Railway Fields | TQ317881 | 2018 |
| Regents Canal | TQ363824 | 2012 |
| Rothamsted Farm | TL121137 | 2010 |
| Roughdown Common (Lower) | TL048055 | 2018 |
| Roxbourne Rough | TQ120875 | 2018 |
| Sherrardspark (Red Lion to Reddings) | TL224140 | 2016 |
| Sherrardspark (Reddings) - 2010 route | TL230135 | 2016 |
| Sherrardspark (Sixways Mid Section) | TL230134 | 2016 |
| Sherrardspark (Templewood Vale - Muddy Bottom to Pentley Park Entrance) | TL235142 | 2015 |
| Sherrardspark (Templewood Vale - new) | TL235143 | 2018 |
| Sherrardspark Wood - Sefton | TL228138 | 2016 |
| Shrubhill Common | TL036072 | 2018 |
| Smallford Lake | TL194071 | 2009 |
| St James Park/Green Park | TQ295798 | 2018 |
| Stevenage | TL246234 | 2018 |
| Stockers Lake 2012 | TQ045935 | 2018 |
| The Warren | TL204053 | 2017 |
| Therfield Heath (Base of Church Hill) | TL333395 | 2018 |
| Therfield Heath (Church Hill) | TL333396 | 2018 |
| Therfield Heath (Lankester Hill) | TL353404 | 2018 |
| Therfield Heath (Rifle Range) | TL348401 | 2018 |
| Therfield Heath (Top of Rifle Range) | TL349398 | 2018 |
| Thorley Wash | TL489181 | 2017 |
| Tottenham Wildmarsh West | TQ351905 | 2015 |
| Totteridge Fields | TQ222940 | 2018 |
| Tower Hamlets Cemetery Park | TQ366823 | 2018 |
| Trent Park Country Park | TQ285965 | 2017 |
| Tring Park (9 sections) | SP927100 | 2018 |
| Walpole Park | TQ173802 | 2018 |
| Ware Park | TL347143 | 2018 |
| Waterford Heath North | TL315152 | 2018 |
| Waterford Heath South | TL317149 | 2018 |
| Wingrave Road | SP926127 | 2012 |
| Wolf Fields | TQ128786 | 2017 |
| Wood Lane Pirton | TQ143312 | 2018 |
