GIS Notes - Mapping Our World PDF

GIS Notes! Defining GIS & Maps What is GIS → A Geographic Information System is A computer‐based information system that enables the Capture, Modeling (representation), Storage, Retrieval, Sharing, & Manipulation Five M’s - Cartography Prediction, processes, w...

GIS Notes! Defining GIS & Maps What is GIS → A Geographic Information System is A computer‐based information system that enables the Capture, Modeling (representation), Storage, Retrieval, Sharing, & Manipulation Five M’s - Cartography Prediction, processes, what if? Distance, area, changes Location, placements, operations Changes over time and space Database Management Systems (DBMS) - software containing multiple databases allowing querying, updating, report generation, and administration Relational DBMS – Use parcel # to find Year Built in separate table GIS Breakdown → - Formal, computerized systems (hardware and software programs) collecting, storing, and processing data so Humans can generate information. They usually use collections of _____________________________ - Basically, a collection of digital tables than can be linked up to other tables and queried for records of interest. - Observations/individuals - Geometries with known locations on Earth are stored with their attributes to be displayed, linked, and manipulated in software packages known largely as geographic information systems. - Can find features of interest (queries) - Extract, append, edit, update, and even automate Types of GIS software - Geobrowser (weak), Web-based (medium), Desktop (strong) Function?: An organization will use/manage many data layers or themes GIS Representation Basics How to incorporate geography into a computer application? - Creating _____________________________________ - A relational Database Management System (DBMS | Nerd Alert!)  How do we describe geographical features? - Combining two types of data: - Spatial - Attribute Decisions on data properties - Projection, scale, accuracy, and resolution - Goes back to the basics of mapping Cartography - What is it? - “...the art, science, and technology of making maps together with their study as scientific documents and works of art.” ▫ British Cartographic Society - Cartography and Change - Computer revolution ▫ ‒ Internet ▫ What is a map?: Geographical representation of locations, objects, themes, & relationships on Earth in a planar format (flat). All maps are abstractions (generalized) Components of a map: ○ Title, Explanatory text, main map, inset, orientation, author, sources!!!, legend, scale, & neatline. 4 Principles: ○ Scale (ratio) Small scale shows more of earth (1:250,000) large scale maps are more “zoomed in” (1:50,000) ○ Location Global coordinates: Longitude, Latitude, Degree, Minute, & Decimals. Lines of Latitude ○ Angle from center of earth and equator. ○ Parallel and almost equidistant – 68.703 miles at the equator – 69.407 miles near poles Lines of Longitude ○ Angle from center of earth to prime meridian ○ Not Parallel ▫ Converge Not Equidistant ○ 69 miles at equator ○ 53 miles at 40° latitude ○ 49 miles at 45° latitude (x,y) from geometry, can have Latitude-Longitude-Elevation  ○ Projection Old School: ‒ Shine a light through it then trace on “developable surface” ‒ Change the position of the light Change the distortion of the map ○ Symbology Geographic coordinate systems - GCS (The Data) - Scheroid (3D) Model; coordinates in lat-long - Datum: spheroid model of the earth with parameters/measurements - Mimicking shape of the earth - Display lat-long on a square grid, origin at Prime Meridian-Equator 1. Flat earth (2D) model; Projection type e.g. Mercator - Create an origin and grid, coordinates in meters or feet - Datum: spheroid model of earth with parameters Coordinate systems in GIS Two key practical issues: 1. How do we store “where” data in files? 2. How do we get data using different coordinate systems to line up? Projections in ArcGIS Locations in GIS files Can be stored in either: - Geographic Coordinates systems (GCS) - Coordinates are in lat-long - Projected Coordinate system - Coordinates are in x, y or easting and northings > Map > Properties > Coordinate System > (Change Projection) How two line up data in GIS 1. “On-the-fly” projection - Let ArcMap handle lining up data sets - Works well for most things and for cartography - What we use in this class 2. Manually “projected” - Use “project” tool in ArcToolbox to re‐project all datasets - Required when doing more analysis & geoprocessing - Future GIS classes On-the-fly - Does math behind the scenes to line up data - Add your datasets to ArcMap - It will read spatial referencing data  - Applies the setting of the first dataset to the data frame - You can alter Map frames to the different coordinate systems. - ArcMap will adjust all data “on‐the‐fly” ‒? ‒ Only in the memory of your project file (.aprx) Things can (and do) go wrong - If data sets done line up, coordinate system error somewhere - Something not defined correctly - Hard to find and fix - Key mistake: Do no change coordinate system in catalog properties - It’s like being told to run 5k but you decide it's really 5mi Projection types: Plate Carree - Simplest projection Easting = latitude Northing = longitude ArcMap’s default projection for geographic coord system data Distance east-west: ugly Universal Transverse Mercator (UTM) - based on the Transverse Mercator projection, which presents the Earth's surface as if projected onto a cylinder wrapped around the globe. Reviewing “where” in GIS Many ways of definition glocation of earth - coordinate system Spatial referencing - the holy trinity - Datum - Approximate the Earth’s shape and use lat‐long for positions. (3D model) - Projection - Flatten it out somehow. - Coordinate system - Put a defined grid over it/Unit of measurement & an origin to document Data Models ‐ Vector How do we represent the world on a computer? - Vector - Points, lines, polygons - Discrete data - Attributes in tables  - Raster - Grids, cells, matrices - Continuous data - Attributes in cell value or table Data Models: What are they? Ways of putting or representing reality in the computer Geographical variation - reality - is infinitely complex Couldnt represent it all (and wouldn't want to) Need to specify at least 2 things - Location (coordinates to describe location/boundary) - Identify (one or more description, or attributes, of the object) - May also specify a third: Relationships (spatial relationships, or topology, between objects) “What” - attribute tables - Data about objects stored in an attribute table - Columns called fields - Rows called records - Typically, one or more fields for international use, e.g. ObjectID - Can specify anything about objects that is relevant - texts , numbers, Word files, URLs, even photography Vector data model: Basics Point - Singe X and Y coordinate pair Line - String of X and Y coordinate paris] - Order may indicate direction Polygon - String of X and Y coordinate pairs with the same start and end point - Or may be set of connected lines “Multipart” (Point, line, or polygon) - Make up of servaer points Types of vector files: Shapefile - Can only hold points, lines, or polygons - Not combinations - one geometry type at a time - Made up of several files working together - (.shp,.dbf,.prj,...) - Smple, but limited; works in multiple GIS programs Types of vector files: Geodatabase - Full power (and complexity) of database - Can hold topology - relationships between geometries - Multiple point, polyline and polygon data sets - Advanced capabilities - Stored as a folder with *.dged or *.mdb extensions - How most newer data is being stored Geodatabase & data -.gdb is like a container or folder - Feature dataset - Can have multiple layers - Same area - Same spatial referencing - Can set up rules to check errors - Feature class - Themes of same geometry - Raster datasets Vector model: Advantages Pros - More appropriate for discrete features - Maintains shapes better - More precise locations - More efficient to store on computer - Useful at a wide range of scales Cons - More time editing and building topology requirements more time and editing, increases cost - Analyses of vector layer more computationally intensive - Continuous data is difficult to represent Conclusion/Review - Data model not reality - its a limited, conceptual view - Data model contains - Where - coordinates - What - attributes - Topology - relationships Thematic Maps and GIS Types of maps: “Tangible” - starting to blend with visuals General reference - overall depiction of an area ○ Most commonly when thinking of maps ○ Hard to make ○ Important “human” places Cons of general reference: lots of data, hard to interpret, can't add much. Thematic - more selective with data shown. ○ Numbers and category display Symbology: turning attributes into geographical codes ○ Most prevalent type of map Many are use poor methods to show data ○ Choices of symbols & colors depend on data what would be interpretable? Choices! Thematic Map: Communicating Data! ○ How to Represent data: Choropleth map - symbolize data with colors Divide into classes Each class is shaded/colored uniquely Optimally 3 to 7 classes Dot-density map - symbolize data with density of single symbol Proportional symbol map - symbolize data with varying size symbol Many MORE! Data Types ○ Qualitative (Names, categories, classifications) vs Quantitative (numbers) 1. Nominal - Names  2. Ordinal - Ranking (number) 3. Interval - Lack a clear 0 value, but differences between values are meaningful. 4. Ratio - has meaningful zero and differences are also meaningful. Geographic Codes ○ Shape, size, color/hue, color lightness, color saturation, & texture Data Models & Theomatic Mapping Tables & Vector Data Files Shapefiles: Attributes and location saved on separate files. Uses Featured ID (FID) - Unique identifier for software Shape_area/Shape_field do not keep track of the areas and lengths of features. Geodatabases: Attributes to location saved in same file Uses Object ID (OID) – Unique Identifier for software Shape_area/Shape_field keep track of the areas and lengths of features! Stand-alone tables: Plain text, attributes (i.e., Excel, text file, etc) Object ID (OID) generated\ Tables to Maps 1 Display XY Data Cooridnate pairs - dots on maps Geocoding Converting addresses and turning into points Can be complicated and expensive\ Field Name Conventions - 13 or fiewer characters - Only letters, numbers, and underscores Field Types - Set to data formats - Once a field definition is set and saved, it connot be changed. - More common types - Numbers - Intergers: Short and Long - Decemals: Float and Double - Text: define field length → number of characters sorted - Dates, etc Create New Fields or data - Use “Add field - Switch to Fields View - Create so,[;e ma,e. Alias can be longer - Select a field type based on what will be stored - Interger (short or long) - Real number ( float or double - Text, Date, etc Calculate geometry - Add information - Field must already exist - Coose a coordinate system and area units to generate - Saves in the table for each feature Calculating Values Ways to change values into table - Typing directly into fields - Field calculator: using values of existing fields - Attribute table → Right-click on filed name