Spatial Analysis – vector data analysis Lecture 8 10/12/2006

Spatial Analysis tools in ArcToolBox Shapefile & Feature class Coverage Raster

Details Shapefile and feature class Coverage Raster

Extract To create a new subset from the input (features and attributes in a feature class or table) based on spatial intersection or an attribute query. Clip Select Split Table select only

Clip ff

Select

Split

Overlay Joining two existing sets of features into a single set of features to identify spatail relationships between the input features. Erase Identify Intersect Symmetrical difference Union Updata

Proximity Identify features that are closest to one another, calculate the distances around them, and calculate distances between them. Buffer Multiple ring buffer Near Point distance

How to form Thiessen polygons Also known as 'Voronoi networks' and 'Delaunay triangulations', Thiessen polygons were independently discovered in several fields of study, including climatology and geography. They are named after a climatologist who used them to perform a transformation from point climate stations to watersheds. Thiessen polygons can be used to describe the area of influence of a point in a set of points. If you take a set of points and connect each point to its nearest neighbour, you have what's called a triangulated irregular network (TIN). If you bisect each connecting line segment perpendicularly and create closed polygons with the perpendicular bisectors, the result will be a set of Thiessen polygons. The area contained in each polygon is closer to the point on which the polygon is based than to any other point in the dataset.