Geographic Information Systems (GIS) Basics

• Module M.SIA.I14M covers GIS and Remote Sensing for Agriculture.
• The initial lesson is an introduction to GIS.
• Dr. Jayan Wijesingha can be contacted via [email protected] or at +49 561 804-1245, located in Room 1004, Steinstrasse 19.

How it Started

• John Snow's 19th-century cholera map of London demonstrated how disease outbreaks could be understood through data journalism.
• The map served as a model for data journalists.

Core Concepts

• GIS utilizes cognitive schemes for geospatial analysis.
• Key elements include location, spatial distributions, regions, hierarchies, networks, spatial associations, and surfaces.

Defining GIS

• GIS, strictly speaking, is a computer system for assembling, storing, manipulating, and displaying geographically referenced data.
• According to USGS, a total GIS involves operating personnel and the data within the system.
• ESRI defines a geographic information system (GIS) as a computer-based tool for mapping and analyzing existing features and events on Earth. GIS integrates database operations, query, statistical analysis, visualization, and geographic analysis.
• NASA describes GIS as an integrated system involving computer hardware, software, and trained personnel, which connects topographic, demographic, utility, facility, image, and other geographically referenced resource data.

GIS Explained

• GIS means Geographic Information System/Science.
• GIS is a multi-component environment for creating, managing, analyzing, and visualizing spatial and non-spatial data.

Applications of GIS

• GIS is applied to urban planning, disaster risk management, logistics, public health, and agriculture.

GIS Components

• Key components include hardware, software, data, and people.

GIS Operations

• Real-world features are represented by layers in GIS.
• Layers contain both spatial (x, y) and attribute data (id, name, year, etc.).
• Multiple layers can be overlaid.
• Analyses are conducted based on location (spatial) and attributes (aspatial) data.

Representing Real-World Features

• GIS uses abstraction to represent real-world features.
• Two main representation types are vector and raster.

Vector Data

• Vector data represents features with points, lines, and polygons.
• Geometry is defined using one or more vertices.
• The position of a vertex is described using X, Y, and/or Z coordinates.
• Each vector feature includes attribute data.

Vector Data Components

• Vector data is composed of features, geometry, and attributes.
• Geometry is divided into Point, Polyline, and Polygon.

Point Features

• A point is a single vertex used to represent objects as shape-less, size-less 1D features.
• Selection of an object to represent depends on spatial extent.
• Cities can be shown as points on a district map.

Line Features

• Line features represent 1D objects: roads, railroads, canals, rivers, and powerlines.
• A line feature can be a 2D polygon, depending on the scale.
• A line comprises two or more vertices, depending.

Polygon Features

• Polygons represent enclosed areas like lakes, cities, islands, and countries.
• Polygons contain multiple vertices.
• To form an enclosed polygon, the first and last vertices share the same coordinates.
• Adjacent polygons have shared geometry.

Attribute Data

• Attribute data is non-spatial information linked to a spatial object.
• Attribute data types include integer, float, text, and logical.

Vector Data Capture

• Methods include digitizing existing paper maps, surveying, and extraction based on aerial/satellite images.

Map Scale

• Map scale affects the level of detail that can be represented.
• Examples show digitization from scales of 1:1000 000 and 1:50 000.

Vector File Formats

• Common formats include ESRI Shapefile, GeoJSON, GML, SpatiaLite, and Geopackage.

ESRI Shapefile

• ESRI Shapefile was introduced and managed by ESRI (Environmental Systems Research Institute).
• It is a file-based data format.
• A single shapefile consists of multiple files:
  • .shp: stores feature geometry.
  • .shx: feature geometry index.
  • .prj: coordinate information.
  • .dbf: attribute information.
  • .sbn or .sbx: spatial index.
  • .aih or .ain: attribute index.

GML (Geographic Markup Language)

• GML is a Geographic Markup Language.
• It is an XML-like format for storing different feature types.

Geopackage

• Geopackage is a new format based on open format standards.
• It is compact and stored as a single file with the .gpkg extension.

Raster Data Characteristics

• Raster data represents features/phenomena as a matrix.
• It is mostly used for continually varying information.
• Examples include rainfall, temperature, land cover, and elevation.
• Raster data consists of cells or pixels.
• Each cell has a middle point coordinate and represents a single value.
• Areas without a feature have cells with NULL values.
• Cells are generally square but can also be hexagon or rectangle.
• The value within each cell representing is assumed to be homogeneous.

Spatial Resolution

• Spatial resolution is the smallest distance unit at which a change can be observed.
• Higher spatial resolution means a smaller area represented on the ground.
  • 30 m spatial resolution: divides the area by 30m x 30m cells (900 m² region), seen in SRTM elevation data.
  • 1 km spatial resolution: divides the area by 1km x 1km cells (1km² region), visible in MODIS satellite images.

Raster Data Capture

• Raster data is captured via satellite/aerial images and derived products like land cover/use and elevation.
• Uses Interpolated point observations like rainfall and temperature.
• Converting vector data to raster is another method.

Raster Data File Formats

• Common image file formats: PNG, JPEG (e.g., JP2), and TIFF.
• Binary file formats: band interleaved by pixel (.bip), band interleaved by line (.bil), and band sequential (*.bsq).
• Software-specific file formats: ArcInfo GRID and ENVI header (*.hdr).

GIS Software

• Commercial software: ESRI ArcGIS, MapInfo, ERDAS, ENVI.
• Open-Source software: QGIS, GRASS, GDAL, PostGIS, R/Python.
• Online + Cloud: Google Earth Engine, ArcGIS online.

Basic GIS Analysis

• Basic GIS analysis involves search and visualization.

Search and Visualise

• Attribute search retrieves data using attribute queries, such as cities with a population over 1 million or fields that only grow maize?
• Spatial search retrieves data based on spatial information, such as schools within 1 km or supermarkets within a municipality area.

Distance Measurement

• Euclidean distance (as the crow flies) uses the Pythagorean theorem.
• Distance within network is measured by the sum of each line segment.
• Spherical distance is used for airline routes.

Area of Polygon

• Calculating the area of a polygon relies on vertex coordinates.

Vector Overlay

• Common operations include point in polygon (e.g., biogas plants in Hesse using a ray casting algorithm), line in polygon (e.g., rail road in NVV), and polygon in polygon (e.g., no air-zone within a district boundary).

Buffer

• Buffering is used to address proximity.
• Examples include the area affected after a volcano eruption and no construction zone along a river.

Dissolve

• Dissolve aggregates unit polygons into new ones using selected attributes.

Clip

• Clipping cuts out a portion of one layer using a defined boundary (like a cookie cutter).
• The input layer can be point, line, polygon, or raster.
• The clipping layer must be a polygon.

Additional Tools

• Intersection: Similar to clip but preserves attributes from both datasets.
• Merge combines two datasets of the same datatype.
• Erase (difference) removes the part of a feature that overlaps the erasing feature.

Summary

• GIS is a system for storing, managing, analyzing, and visualizing geographic data.
• Two main types of GIS data are raster and vector.
• Many more spatial analysis tools are available.