Introduction to Geographic Information Systems (GIS)

GIS

A system for capturing, managing, analyzing, and visualizing spatial and geographic data.

Key Components of GIS

Hardware, Software, Data (Vector/Raster), People, and Workflows.

Elements of a map

Title, legend, scale, north arrow, projection, data source, and metadata.

Difference between paper and digital maps

Paper: Static and hard to update. Digital: Interactive and easy to edit/analyze.

Vector Data Model

Represents discrete features using points, lines, and polygons (e.g., cities, roads, boundaries).

Raster Data Model

Represents continuous data using grid cells (e.g., elevation, temperature).

Advantages of the Vector Data Model

High precision, compact storage, ideal for boundaries.

Advantages of the Raster Data Model

Simple for surface analysis, ideal for continuous data.

Raster Resolution

The size of grid cells in real-world units (e.g., 10m x 10m).

Geographic Coordinate System (GCS)

Uses latitude and longitude to locate points on Earth (e.g., 45°N, 90°W).

Projected Coordinate System (PCS)

Projects Earth onto a 2D plane to minimize distortions (e.g., UTM, Mercator).

UTM (Universal Transverse Mercator)

A projected coordinate system dividing Earth into 60 zones for accurate local mapping.

Conformal Projection

A projection that preserves shape (e.g., Mercator).

Equal Area Projection

A projection that preserves area (e.g., Albers Equal Area).

Equidistant Projection

A projection that preserves distances along certain lines.

Azimuthal Projection

A projection that preserves direction from a central point (e.g., Polar Stereographic).

Local Raster Operation

Operates on individual raster cells (e.g., reclassification).

Focal Raster Operation

Analyzes neighborhoods around raster cells (e.g., slope or moving average).

Zonal Raster Operation

Summarizes raster values within predefined zones (e.g., average elevation in watersheds).

Global Raster Operation

Operates across the entire raster dataset (e.g., Euclidean distance).

Topology

Describes spatial relationships (e.g., adjacency, connectivity, and containment).

Adjacency

Features sharing borders (e.g., neighboring states).

Connectivity

Features connected in a network (e.g., roads linking cities).

Containment

Features enclosed within others (e.g., a lake inside a park).

Buffering

Creates zones around features (e.g., a 100m buffer around rivers).

Overlay

Combines spatial layers to analyze relationships (e.g., intersect, union).

Clip Tool

Extracts features from one layer within another's boundaries.

Intersect Tool

Combines overlapping areas from multiple layers.

Union Tool

Combines all features from multiple layers.

Spatial Interpolation

Estimating unknown values using known data points.

IDW (Inverse Distance Weighted)

An interpolation method where closer points have more influence.

Kriging

A stochastic interpolation method that adds randomness and error estimation.

Zonal Statistics

Summarizes raster values within zones (e.g., average temperature in watersheds).

Map Algebra

Combines raster datasets using mathematical and logical operations (e.g., addition, subtraction).

Raster Reclassification

Assigning new values to raster cells based on conditions (e.g., low/medium/high elevation).

Datum

A reference model for Earth's shape (e.g., WGS84).

DEM (Digital Elevation Model)

A raster-based representation of elevation.

Snap Raster

Ensures alignment of grids during raster creation.

Euclidean Distance

Straight-line distance from a point to other cells.

Mixed Pixel Problem

Occurs when a raster cell contains multiple land types.