Basic Spatial Analysis

Extract Tools

The purpose of these tools is to extract features or part of features in an existing dataset and create a new layer containing these features. These tools are also available to work with both raster and vector datasets. In the context of this workshop, we will focus on working with vector analysis.

Clip

Uses a polygon dataset (clip coverage) to determine which features will be extracted to a new layer. Always the outermost polygon is the one that extracts the features, both spatially (acts as a cookie-cutter) and in the attribute table.

Proximity Tools

The Proximity toolset contains tools that are used to determine the proximity of features within one or more feature classes or between two feature classes.

These tools can identify features that are closest to one another or calculate the distances between or around them.

One of the most basic questions asked of a GIS is "what's near what?" For example:

- How close is this voting poll to a train station?

- Do any roads pass within 1,000 meters of a factory?

Buffer

Creates buffer polygons around input features to a specified distance.

An optional dissolve can be performed to combine overlapping buffers.

Quantifying Nearness

- Near

It determines the distance from each feature in the input features to the nearest feature in the near features, within the search radius.

- Point Distance

It determines the distance from input point features to all points in the near features within a specified search radius.

Overlay Tools

A critical function in GIS analysis is the integration of datasets: determining where different geographic phenomena are coincident. Overlay tools are powerful analysis tools for:

• vertical stacking and merging of spatial data

• combine, erase, modify features from multiple datasets

Intersect

Computes a geometric intersection of the input features. Features or portions of features which overlap in all layers and/or feature classes will be written to the output feature class. Intersect combines all the features and attributes of the two inputs, overlaying feature classes.

Union

Computes a geometric union of the Input features. All features will be written to the Output Feature Class with the attributes from the Input Features, which it overlaps.