Lecture 2 - Spatial Data Models & Data Input Methods.pdf

Lecture 2: Introduction to Spatial Data TC 25 GIS University of the Philippines Diliman Department of Geodetic Engineering JBB | AY 2024 - 2025 Training Center for Applied Geodesy and Photogrammetry OUTLINE Spatial Data and D...

Lecture 2: Introduction to Spatial Data TC 25 GIS University of the Philippines Diliman Department of Geodetic Engineering JBB | AY 2024 - 2025 Training Center for Applied Geodesy and Photogrammetry OUTLINE Spatial Data and Data Models Spatial Data Sources Data Input Methods TC 25 BASIC GIS | JBB  Spatial Data and Data Models TC 25 BASIC GIS | JBB  DIGITAL GEOGRAPHIC DATA Numerical representations that describe real-world features and phenomena Must be encoded in digital form and organized as a geographic database to be useful to GIS 4 TC 25 BASIC GIS | JBB  CONVENTIONAL VS DIGITAL GEOGRAPHIC DATA Conventional Data: Paper map Static representation Represents a general-purpose snapshot of the real world at a given time only Digital Geographic Data Dynamic representation Allows a range of functions for storing, processing, analyzing, and visualizing spatial data Has tools that allow users to interact with the data to meet their objectives TC 25 BASIC GIS | JBB 5  WHAT IS A DATA MODEL TC 25 BASIC GIS | JBB 6  RASTER AND VECTOR DATA MODEL FIELD MODEL the world is a continuous field in 2 or 3 dimensions (e.g., surface elevation) OBJECT MODEL Discrete objects –the world is made up of well- defined entities (e.g., buildings, roads) Fuzzy objects – entities with diffused boundaries TC 25 BASIC GIS | JBB 7  TWO DATA MODELS RASTER VECTOR Continuous data represented Geometric features with by grid cells or pixels defined boundaries TC 25 BASIC GIS | JBB 8  TWO DATA MODELS IN GIS TC 25 BASIC GIS | JBB 9  RASTER DATA Each cell can “own” only a single value Multi-attribute data will be 3 3 3 3 3 3 3 3 3 3 1 1 1 1 1 1 1 1 1 1 represented by several 3 3 3 3 3 1 1 1 1 1 raster maps 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 2 2 2 2 2 2 2 2 3 3 2 2 2 2 2 2 2 2 Each raster map will have an individual attribute table 10 TC 25 BASIC GIS | JBB  RASTER DATA MODEL 11 TC 25 BASIC GIS | JBB  RASTER DATA MODEL Best used to represent geographic features that vary continuously over a large area and have no obvious boundaries(e.g. soil type, vegetation, etc.) Uses an array of rectangular cells/pixels/grids to represent real-world objects. Each cell is defined by a coordinate location and an attribute that identifies the feature. Cell’s linear dimensions defines the spatial resolution 12 TC 25 BASIC GIS | JBB  EXAMPLE: DEM DIGITAL ELEVATION MODEL A raster-based representation of the earth’s surface 13 TC 25 BASIC GIS | JBB VECTOR DATA ▪ Attributes stored in a tabular form row = record or object or feature (point/line/polygon) column = property or attribute or field ID Area Site Owner Date Cost ▪ Multiple attributes may be contained in a 1 2 single table, if mapping units remain the 3 4 same 5 6 TC 25 BASIC GIS | JBB 14  VECTOR DATA Columns or fields may be added to with specific data types: NUMBERS: Users specify the precision, which is the maximum length of the field, and scale, which is the maximum number of decimal places. TEXT/STRING : a text field represents a series of alphanumeric symbols DATES: this type can store dates, times, or dates & times. Default format in which information is presented is mm/dd/yyyy hh:mm:ss and a specification of AM or PM TC 25 BASIC GIS | JBB 15 VECTOR DATA MODEL Treats geographic space as populated by discrete objects, which have identifiable boundaries or spatial extent Each object in the real world is represented as either point, line, or polygon features DBF –database file (attribute table) PRJ –projection file * SBN –a spatial index of the features (optimizes spatial queries) ** SBX –a spatial index of the features (speeds up loading times) ** SHP –geometry file (location and shape) SHX –shape index format SHX.XML –geospatial metadata in XML format ** TC 25 BASIC GIS | JBB 16  VECTOR VS RASTER LOCATION REPRESENTATION TC 25 BASIC GIS | JBB 17  VECTOR VS RASTER LOCATION REPRESENTATION Raster Vector TC 25 BASIC GIS | JBB 18 SPATIAL DATA MODELS Raster Vector TC 25 BASIC GIS | JBB 19  WHICH IS BETTER? RASTER OR VECTOR? Source and type of data Intended use of data Analytical procedures to be used 20 TC 25 BASIC GIS | JBB  RASTER ADVANTAGES DISADVANTAGES Simple data structure No precise locational and area computation information due to Easy to conceptualize space grid cells representation Requires large storage capacity Easy data collection and based on size and number of processing colors High spatial variability is Only one attribute per pixel efficiently representAed Loss of information when using large cells Allows easy integration of Blocky appearance when image data (satellite, image is viewed in detail remotely-sensed, etc.) 21 TC 25 BASIC GIS | JBB  VECTOR ADVANTAGES DISADVANTAGES Compact data structure Complex data structure Provides precise locational Difficult overlay operations information of points High spatial variability is Can represent point, line, and inefficiently represented area features very accurately, leading to more accurate Not good at continuous measurements and map coverage or plotters that fill outputs areas Sophisticated attribute data handling (multiple attributes) 22 TC 25 BASIC GIS | JBB  DATA FORMAT: VECTOR ▪ GDF/DIME (Geographic Base File/Dual Independent Map Encoding) – originally used for storing street maps ▪ TIGER (Topologically Integrated Geographic Encoding and Referencing System) – improvement for GDF/DIME ▪ DLG (Digital Line Graphs) – USGS topographic maps ▪ AutoCAD DXF (Data Exchange Format) – widely used as an export format in many GIS ▪ IGDS (Intergraph Design System) – widely used in mapping ▪ ArcInfo Coverage – stores vector graphical data using topological structure explicitly defining spatial relationships ▪ ArcInfo E00 – export format of ArcInfo ▪ Shapefiles – proprietary format; defines geometry and attribute of geographically referenced objects using the main file, index file and database table ▪ CGM (Computer Graphics Metafile) – ISO standard for vector data format; widely used in PC-based computer graphics applications 23 TC 25 BASIC GIS | JBB  DATA FORMAT: RASTER ▪ BMP (bitmaps) – used by graphics in Microsoft Windows applications; no compression ▪ DIB (Device Independent Bitmaps) ▪ GIF (Graphical Interchange Format) – widely used for images to be used on the World Wide Web ▪ TIFF (Tagged Image File Format) – non-proprietary, system-independent ▪ JPEG (Joint Photographic Experts Group) – primarily for storage of photographic images and for the World Wide Web ▪ GeoTIFF – extension of the TIFF format that contains georeferencing information ▪ PNG (Portable Network Graphics) – patent-free; intended to replace the GIF format ▪ PCX – supported by many image scanners ▪ MrSID (Multi-resolution Seamless Image Database) ▪ GRID – proprietary format used by ESRI in ArcInfo and ArcView GIS 24 TC 25 BASIC GIS | JBB  Spatial Data Sources TC 25 BASIC GIS | JBB  SOURCES OF DATA Collect your own data Academe Government agencies Individuals Private companies Internet, Geoportals, Google Earth, NGOs OSM News Telecoms TC 25 BASIC GIS | JBB 26 SOURCES OF DATA GIS integrates data from many sources, of various forms 107’ Vectors Topology Dimensions Surveys ABC Networks Images Annotation CAD Drawings 27 Main St. 3D Objects Addresses Attributes Terrain TC 25 BASIC GIS | JBB 27  PH GEOPORTAL TC 25 BASIC GIS | JBB 28  PROJECT NOAH TC 25 BASIC GIS | JBB 29 DREAM LIPAD TC 25 BASIC GIS | JBB 30 OSM TC 25 BASIC GIS | JBB 31  CATEGORIES: GEOGRAPHIC DATA ACQUISITON ▪ Primary Data Capture Collected through first-hand observation In-house creation of data (any survey, photogrammetry, image analysis) Typically the most expensive part (~80% of project cost) Secondary Data Capture Data collected by another individual or organization; most are published data From maps, reports, previous projects DEMs from topographic map contours, scanned paper maps 32 TC 25 BASIC GIS | JBB  CENSUS AND SURVEY DATA May be spatial in character if each item has a spatial reference, allowing its location on the Earth to be identified Usually in tabular format Examples: population census, employment data, agricultural census data, marketing data 33 TC 25 BASIC GIS | JBB  SATELLITE IMAGES GROUND SURVEY TC 25 BASIC GIS | JBB 34  Data Input Methods TC 25 BASIC GIS | JBB DATA INPUT GIS provides four sets of capabilities: – data input – data management (data storage and retrieval) – manipulation and analysis – data output TC 25 BASIC GIS | JBB 36 WHY CREATE GEOSPATIAL DATA? The data you need has not been created The data you need is on a paper map and needs to be converted to digital format The data available is at a different scale than you need The data available is too old for your purposes TC 25 BASIC GIS | JBB 37 DATA INPUT AND CONVERSION RASTER DATA ACQUISITION VECTOR DATA ACQUISITION Scanning Manual digitizing Photogrammetry Computer-assisted digitizing Remote sensing Field surveying GPS surveying TC 25 BASIC GIS | JBB 38 DATA INPUT AND CONVERSION TC 25 BASIC GIS | JBB 39 DATA INPUT: CONSIDERATIONS The goal is to use the mode of data input that: Best translates the source data to electronic form Is fast Is easy to use Reduces cost Maximizes the accuracy required for the GIS project TC 25 BASIC GIS | JBB 40  DATA INPUT: CONSIDERATIONS COORDINATE DATABASE TOOLS ENCODING REFERENCE MANAGEMENT To transform SYSTEM SYSTEM spatial data of Both locational and attribute data Bring all data to a Attribute data various types into common coordinate often obtained DIGIITAL FORMAT reference system and stored in tables TC 25 BASIC GIS | JBB 41  GIS DATA INPUT METHODS FOUR BASIC PROCEDURES FOR SPATIAL DATA INPUT 1.Image Acquisition 2.Entry of Coordinates using Coordinate Geometry 3.Manual Digitizing 4.Conversion of Existing Digital Data TC 25 BASIC GIS | JBB 42 1. IMAGE ACQUISITION SCANNING Most commonly used method when raster data is required Accuracy depends on the scanner quality (resolution), quality of the image processing software used to process the scanned data, and quality/complexity of source document TC 25 BASIC GIS | JBB 43 1. IMAGE ACQUISITION REMOTE SENSING Photogrammetry (Aircraft, UAV, etc.) Satellite images Google Earth/Maps Bing Maps TC 25 BASIC GIS | JBB 44 2. TEXT FILES / MANUAL ENTRY Can be imported in the software: Text file or table with X, Y or Longitude & Latitude coordinates Data from spreadsheets GPS Data TC 25 BASIC GIS | JBB 45 3. DIGITIZING The process where features on a map or image are converted into digital format for use in GIS. Digitizing converts the features on the map into three basic data types: – Points – Lines – Polygons TC 25 BASIC GIS | JBB 46 3. DIGITIZING TC 25 BASIC GIS | JBB 47 3. DIGITIZING POINT LINE POLYGON TC 25 BASIC GIS | JBB 48 3. DIGITIZING DIGITIZING (VECTOR – NETWORK DATA) TC 25 BASIC GIS | JBB 49 3. DIGITIZING In creating vector data, the topology should be well-defined. TC 25 BASIC GIS | JBB 50 3. DIGITIZING COMMON SPATIAL ERRORS ▪ Slivers or gaps in the line work; missing points, line segments, and polygons – Dead ends, dangling arcs, overshoots and undershoots. – Bow ties or weird polygons caused by inappropriate closings of connecting features TC 25 BASIC GIS | JBB 51 COMMON ERRORS IN DIGITIZING ▪ Location placement ▪ Incorrect linkage between spatial errors of spatial data; and attribute data careless digitizing or poor - misplaced labels or unique identifiers quality of the original being assigned during manual key entry source. or during the initial setup. ▪ Attribute data is wrong or ▪ Redundant incomplete; missing data information, including records or data records vertices, text, nodes, from different time and arcs. periods. TC 25 BASIC GIS | JBB 52 MANUAL DIGITIZING Errors are usually due to: Incorrect registration of map features on the digitizer table (‘hand-wobble’) –Time-consuming and tedious, especially for a large amount of data TC 25 BASIC GIS | JBB 53  ON SCREEN DIGITIZING (HEADS UP DIGITIZING) COMBINATION OF SCANNING AND MANUAL DIGITIZING The main steps in heads up digitizing typically include: 1. Scanning the map 2. Registering the map – add position to map 3. Digitizing the map – trace features on the map. TC 25 BASIC GIS | JBB 54  ON SCREEN DIGITIZING (HEADS UP DIGITIZING) COMBINATION OF SCANNING AND MANUAL DIGITIZING The maps are already in the correct geographic coordinate system, anything digitized on the map will also be in the correct coordinate system. TC 25 BASIC GIS | JBB 55 Additional Notes: Cartography TC 25 GIS University of the Philippines Diliman Department of Geodetic Engineering JBB Training Center for Applied Geodesy and Photogrammetry CARTOGRAPHY science and art of making maps and charts A depiction of all or part of the earth or other geographic phenomenon as a set of symbols and at a scale whose representative fraction is less than one to one An abstraction of reality for analyzing, storing, and communicating information about locations, attributes, and interrelationships of physical and social phenomena TC 25 BASIC GIS | JBB 57 ABSTRACTION OF REALITY (MAPS) We typically generalize the real-world using: points, lines, and polygons. TC 25 BASIC GIS | JBB 58 MAPS VS GIS TC 25 BASIC GIS | JBB 59 MAPS Mapping is a key output of GIS but is not the whole story GIS GIS stores the spatial data (used to make maps) GIS is an analysis tool. TC 25 BASIC GIS | JBB 60 MAP ELEMENTS COORDINATE LEGEND OTHERS MAP SCALE SYSTEM TC 25 BASIC GIS | JBB 61 MAP ELEMENTS ratio shows the relationship between the map unit and the real-world unit. to better visualize the distances and other lengths in the map MAP SCALE TC 25 BASIC GIS | JBB 62 MAP ELEMENTS Coordinate Reference System and Direction/Orientation indicators denote the location measures used in the map and the actual North orientation COORDINATE SYSTEM TC 25 BASIC GIS | JBB 63 MAP ELEMENTS This is the guide or key to the information found on the map. It explains the meaning of the symbols used. LEGEND TC 25 BASIC GIS | JBB 64 MAP ELEMENTS Other important information that will be useful (and sometimes required) to explain the contents of the map OTHERS TC 25 BASIC GIS | JBB 65 THANK YOU! QUESTIONS? [email protected]