In the property world, a contour is an outline of a mass of land. A contour or detailed survey is done by a surveyor and required before you can start on the design of your buildings. Contour lines will be marked on the survey. Below are some tips* that can help explain the marking you’ll see:
- All points on a contour line are of the same elevation.
- No two contour lines can meet or cross each other except in the rare case of an overhanging vertical cliff or wall
- Closely spaced contour lines indicate steep slope
- Widely spaced contour lines indicate gentle slope
- Equally spaced contour lines indicate uniform slope
- Closed contour lines with higher elevation towards the centre indicate hills
- Closed contour lines with reducing levels towards the centre indicate pond or other depression.
- All contour lines must close either within the map boundary or outside.
Once the architect or draftsperson has a contour survey then they can begin work on the plans and the survey will indicate how much site works may be required. For example, a sloping site will need to be levelled if you are using a slab construction and therefore the approximate height of retaining walls and volume of spoil to be removed need to be calculated. These costs need to be allowed for by the builder and he depends on the measurements on the contour survey for this data.
Accuracy of a survey is extremely important. On one site we found the surveyor (not mine, as this was a DA approved site purchased) had taken a measurement from one meter in from the rear boundary instead of right on the rear boundary. This was not picked up until after site preparations started and the site was cut. As the site sloped from rear to front, the retaining required on this rear boundary was much more than the builder had allowed for based on the plans. So it is important if you are buying DA approved sites, to have your own surveyor double check the plans and proposed levels which are based on the original contour survey.
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