GIS Fundamental Tasks Lecture 13 PDF

LECTURE 13 GIS Fundamental Tasks KEY PROPERTIES OF SPATIAL DATA  Projection: Converts 3D Earth to a 2D map (distortion is always present)  Scale: The ratio of map distance to ground distance  Accuracy: Ensures data reflects the real world  Positional: how close are features to their real-w...

LECTURE 13 GIS Fundamental Tasks KEY PROPERTIES OF SPATIAL DATA  Projection: Converts 3D Earth to a 2D map (distortion is always present)  Scale: The ratio of map distance to ground distance  Accuracy: Ensures data reflects the real world  Positional: how close are features to their real-world location?  Consistency: do feature characteristics in database match those in real world  Completeness: are all real-world instances of features present in the database?  Resolution: Represents the smallest feature recognizable on a map, especially in raster data GIS TASKS  GISs essentially perform five tasks or processes:  Input  Manipulation  Management  Query and Analysis  Output (visualisation/display) 1. INPUT (DATA ENTRY)  Data input is the operation of encoding data for inclusion into a database  First step in using GIS – creation of accurate databases is a very important part of GIS  Success of any GIS project depends on the quality of the data entered  GIS integrates a variety of data types from a variety of sources. Two main sources:  Primary – collected directly in digital format specifically for GIS use (e.g.: remote sensing images, GPS and field survey data)  Secondary – digital and analog datasets that were originally captured in another format (paper) and needs to be converted to digital GIS data formats (through digitising, scanning) MANIPULATION  For some GIS projects, collected data will need to be transformed or manipulated to make them compatible with each other and/or the program being used  For e.g., geographic information is available at different scales (1:100,000; 1:10,000; 1:50,000) – needs to be transformed to same scale before it can be overlaid and integrated  All data needs to be at the same scale, coordinate system, format, etc.  Transformation can be temporary (display purposes) or permanent (analysis)  Types of data manipulation include projection changes, data aggregation, generalization and weeding out unnecessary data 2. MANAGEMENT (DATA STORAGE)  Database – structured collection of data files (tabular data in rows and columns)  database management system (DBMS) is used to help store, organize, and manage data  DBMS – software package that allows for the creation, storage, manipulation and retrieval of large datasets distributed over one or more files  many different designs of DBMSs, but in GIS the relational design has been the most useful  relational design – data are stored conceptually as a collection of tables. Common fields in different tables are used to link them together GEODATABSE  Geographic information can be stored and managed in geodatabase (GDB)  GDB – geo (spatial) and database (relational DBMS)  GDB allows for GIS data to be stored uniformly in a central location – easy access and management  Supports all the different types of GIS data (attribute, geographic features, satellite and aerial images (raster) GPS coords, etc.)  Storing GIS data in GDB allows users to easily create detailed more detailed and accurate spatial data models 3. QUERY  Query – the ability to ask and answer questions about geographic features and their attributes and the relationship between them  Allows user to retrieve a subset of data from the DBMS using Structured Query Language (SQL – computer language used to query, or ask questions of, a database via an established structure of expressions)  Two main types of queries:  Database queries (select by attribute)  Spatial queries (select by location) https://www.esri.com/news/arcuser/0309/files/rightqueries.pdf DATA QUERYING – SELECT BY ATTRIBUTE  Allows you to provide a SQL query expression that is used to select features from the attribute table that match the selection criteria  For example, if you want to select the KZN provincial boundary from the South_Africa country layer which has all provincial boundaries, you would create the following query SELECT FROM South_Africa WHERE “PROVINCE” = “KZN”  Many different attribute queries can be created based on the application DATA QUERYING – SELECT BY LOCATION  A tool that lets you select features based on their location relative to features in another layer  For example, if you want to know how many homes were affected by a recent flood, you could select all the homes that fall within the flood boundary of a rivers layer  Many different selection options eg. intersect, within can be used for different queries 4. ANALYSIS (SPATIAL ANALYSIS)  Spatial analysis is one of the most important aspects of GIS  Allows users to combine data from different sources, model problems geographically and derive new sets of info by computer processing. Results are then explored and examined (interpreted)  Uses the geographic properties of features to:  Answer complex spatial questions  Look for significant patterns or trends (hidden)  Analyse various layers to calculate suitability for a particular activity  Detect change over time (image analysis)  Spatial analysis enables users to answer important questions and make decisions for problems that are beyond the scope of simple visual analysis ANALYSIS  Spatial analysis operations are different for vector and raster datasets:  Vector analysis – Buffering (proximity analysis), Overlay and Distance measurement  Raster analysis – Reclassification and Distance measurement https://learn.arcgis.com/en/arcgis-book/chapter5/ VECTOR ANALYSIS (BUFFERING)  Answers the questions: “What’s near what?” (proximity analysis)  Buffering creates buffer zones by measuring straight-line distances from selected features (points, lines or polygons)  Accuracy of output depends on same measurement units  Buffering output – buffer zone (new feature) represented as a polygon BUFFERING APPLICATIONS VECTOR ANALYSIS (OVERLAY)  Answers the questions: “what’s within what? What’s on top of what? What is overlaying what?”  Overlay creates an output by combining geometries and attributes from different layers (either vector or raster). Combine the characteristics of several datasets into one  GIS software allows us to query and analyze large amounts of data in relation to each other across space  Overlays layers to create a new map to reveal new valuable info  Output accuracy depends on the same coordinate system  Output combines two (or more) different layers to form a new layer (different geometry and attribute table) RASTER ANALYSIS (RECLASSIFICATIO N)  Reclassification is the process of reassigning one or more values in a raster dataset to new output values  helps simplifying raster data (hence making the results easier to interpret)  commonly used to assign different categories in a raster STATISTICAL ANALYSIS  Statistical analysis helps you extract additional information from your GIS data that might not be obvious  Information such as how attribute values are distributed, whether there are spatial trends in the data, or whether the features form spatial patterns  We use statistical analysis to  explore data – for example the frequency distribution of values for a particular attribute. Eg. percentage of senior citizens  summarize data - for example descriptive statistics (mean, std. deviation, count, sum) of a particular attribute. Eg. mean elevation in a DEM  identify and confirm spatial patterns – such as the center of a group of features, the directional trend, or whether features form clusters. Eg. the mean center of a set of burglaries 5. OUTPUT (VISUALISATION)  GIS can provide hardcopy maps, statistical summaries, modelling solutions and graphical display of maps for both spatial and tabular data.  For many types of geographic operations, the end result is best visualized as a map or graph.  Maps are very efficient at storing and communicating geographic information.  GIS provides new and exciting tools to extend the art of visualization of output information to the users.  Map displays can be integrated with reports, three-dimensional views, photographic images, and other output, such as multimedia. https://www.esri.com/arcgis-blog/products/arcgis/3d-gis/gis-visualization-and-storytelling-in-3d/