The method for calculating the area depends on the shape of the property and the information you have available. If you have a survey then you probably have sufficient information. If the borders of the property are straight lines, you know their lengths and you know the angles at the corners then there is a method you can use. Join some of the corners by straight lines to divide the property into non-overlapping triangles. Using the angle measurements and some trigonometry, perhaps the law of cosines, you can determine the lengths of the sides of the triangles. Once you have the lengths of the sides of the triangles you can find their areas using Heron's formula. The area of your property is then the sum of the areas of the triangles.
You can see an example in the answer to a previous question.
I hope this helps,