Modeling Our World

PUBLISHED BY Environmental Systems Research Institute, Inc. 380 New York Street Redlands, California 92373-8100 Copyright © 1999 Environmental Systems Research Institute, Inc. All rights reserved. Printed in the United States of America. The information contained in this document is the exclusive property of Environmental Systems Research Institute, Inc.This work is protected under United States copyright law and the copyright laws of the given countries of origin and applicable international laws, treaties, and/or conventions. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or recording, or by any information storage or retrieval system, except as expressly permitted in writing by Environmental Systems Research Institute, Inc. All requests should be sent to the attention of Contracts Manager, Environmental Systems Research Institute, Inc.,380 NewYork Street, Redlands, California 92373-8100 USA. The information contained in this document is subject to change without notice. ESRI, MapObjects,ARC/INFO, and ArcView are trademarks of Environmental Systems Research Institute, Inc., registered in the United States and certain other countries; registration is pending in the European Community.ArcInfo, ArcMap, ArcCatalog, ArcObjects, AML,ArcSDE,ArcIMS,ARC GRID,Arc Explorer, and the ESRI Press logo are trademarks and www.esri.com is a service mark of Environmental Systems Research Institute, Inc. The names of other companies and products mentioned herein are trademarks or registered trademarks of their respective trademark owners. Environmental Systems Research Institute, Inc. Modeling Our World The ESRI Guide to Geodatabase Design ISBN 1-879102-62-5 U.S. Government Restricted/Limited Rights Any software, documentation, and/or data delivered hereunder is subject to the terms of the License Agreement. In no event shall the U.S. Government acquire greater than RESTRICTED/LIMITED RIGHTS. At a minimum, use, duplication, or disclosure by the U.S. Government is subject to restrictions as set forth in FAR §52.227-14 Alternates I, II, and III (JUN 1987); FAR §52.227-19 (JUN 1987) and/or FAR §12.211/12.212 (Commercial Technical Data/Computer Software); and DFARS §252.227-7015 (NOV 1995) (Technical Data) and/or DFARS §227.7202 (Computer Software), as applicable. Contractor/ Manufacturer is Environmental Systems Research Institute, Inc., 380 New York Street, Redlands, California 92373-8100 USA. Preface All geographic information systems (GIS) are built using formal models that describe how things are located in space. A formal model is an abstract and well-defined system of concepts. It defines the vocabulary that we can use to describe and reason about things. A geographic data model defines the vocabulary for describing and reasoning about the things that are located on the earth. Geographic data models serve as the foundation on which all geographic information systems are built. We are all familiar with one model for geographic information—the map. A map is a scale model of reality that we build, using a set of conventions and rules (for example, map projections, line symbols, text). Once we construct a map, we can use it to answer questions about the reality it represents. For example, how far is it from Los Angeles to San Diego? Or, what cities lie along the Mississippi River? The map model also serves as a tool for communicating facts about geography visually: Is the terrain rough? Which way is north? In fact, when we see a map, we often understand things that might not even occur to us as specific questions. Maps work because we know the “rules” of conventional map reading: blue lines are rivers, North is toward the top of the page, and so on. In a similar way, geographic data models define their own set of concepts and relationships, which must be understood before you can expect to create or interpret your own data model. These concepts relate to how you can represent geographic information in a computer system, rather than, as in the map example, on paper. In Modeling Our World, Michael Zeiler has written an excellent primer for understanding the various models used to represent geographic information in ArcInfo™ 8 software. He presents, using straightforward text and excellent illustrations, the concepts and vocabulary employed in the design, implementation, and use of the ArcInfo 8 geographic database. In addition to explaining the ArcInfo data model (objects, features, surfaces, networks, images, and so forth) in detail, Michael also provides good insight into how to use this framework to design useful information models that fit your particular needs. This book serves a variety of different purposes. For the geographer or scientist, it defines a conceptual context for representing geographic information. For the GIS specialist, it serves as a guidebook in designing and using geographic databases. Finally, it introduces database concepts to a geographic audience, and geographic concepts to the database specialist. ArcInfo 8 defines a unified framework for representing geographic information in a database. Several different generic data models are supported within this framework: · cell-based or raster representation · object-based or feature-based representation · network or graph-element representation · finite-element or TIN representation Each of these generic models has its own vocabulary used to define and reason about geographic information. When we decide to represent roads, rivers, terrain, or any sort of phenomena in a GIS, we need to decide exactly how we define information in terms of these generic models. As chapter 1 points out, there are many ways that information can be modeled in a GIS. The representation you choose for the data model will affect how you sample and measure geographic information, how you display it visually, and which relationships between elements can be represented, as well as query and analysis operations that can be applied to the information. Some have asserted that we should hide representational models for geographic information (features, geometry, rasters, surfaces, and so on) from the users of geographic information systems. Somehow, these representational concepts are considered “implementation details.” In this view, a single real-world thing, such as the Mississippi River, should be modeled as a single thing within the GIS. Perhaps, behind the scenes, the system could automatically use multiple representations for these real-world things. If you ask “What is upstream?” it could use a network representation of the river. If you ask “What is the surface area of the water?” it could use a polygon feature representation. If you ask “What area does it drain?” it could use a surface or terrain representation, and so on. While it may be desirable to hide these concepts from some consumers of geographic information, I believe that a strong understanding of geographic data models and representations is crucial to the correct design and use of geographic information systems. Geographic data models act as the lens or filter through which we perceive and interpret the infinite complexity of the real world. It is only in the context of representations of the Mississippi River, for example, that we can define specific properties, behavior, or even its identity as a “thing of interest.” Understanding geographic data model concepts is central to knowing how to define and collect geographic information. It is also crucial for correctly interpreting the results derived from the analysis of geographic information. This is similar to the role that statistics and sampling theory play in the natural sciences. For the GIS specialist, this book serves as an introduction to a new object-relational model for representing features, spatial relationships between features, and other thematic relationships. This new model is significantly richer in its ability to represent features with associated behavior, relationships, and properties than the current coverage or shapefile model. If you are already familiar with coverages, shapefiles, and database tables, the new model is a dramatic extension of concepts and capabilities with which you are already familiar. Our goal in building the new feature data model has been to move as much specialized application logic (for example, maintaining connectivity or relational integrity between objects) as possible into the scope of the data model itself. This allows more of the GIS application to be defined using rules in the data model, rather than custom application logic written for each application. For other aspects of the data model, which may already be familiar to the reader, the specific jargon and concepts used in ArcInfo 8 (for topics like image data, as an example) are clearly introduced and defined. This book also connects the specialized world of geographic information systems and the broader world of object-relational databases. ArcInfo now supports the direct use of standard relational database technology as an integral part of the GIS. This introduces some new concepts to the GIS community. Topics such as transaction models for simultaneous editing of a shared, seamless database are described in detail. For the GIS specialist, this provides a good introduction to standard database concepts. For the database specialist, this book serves as a good answer to the question “what is so special about spatial?” Working with geographic information systems is fun for me because it serves to integrate concepts and ideas from a variety of different disciplines— geometry and networks from applied mathematics, sampling and measurement theory from remote sensing and physics, information modeling and multiuser database issues from information technology. In working with GIS, we get to integrate all of this in a single, useful framework for building real systems. This book presents that synthesis, based on our work with ArcInfo 8. I hope you find this book useful and stimulating as a basis for your own work in geographic information systems. Scott Morehouse Director of Software Development Environmental Systems Research Institute, Inc. Redlands, California Acknowledgments This book, Modeling Our World, is the distillation of many people’s inspirations, ideas, and labors. Many deserve recognition—the ArcInfo user community, which always amazes us with creative applications of GIS; the ArcInfo 8 development team, which has produced a true masterpiece of software; and the teams throughout ESRI, which collaborated to take GIS technology to new levels. Because of the constraints of space, only a few can be directly acknowledged. These are some of the contributors to this software release and book. The structural design of ArcInfo 8 was led by some of the brightest thinkers in the industry. Sud Menon directed the architectural design of the geodatabase and he is responsible for many of the insights expressed in this book. Jeff Jackson led the implementation of software component technology that has revolutionized ArcInfo. Erik Hoel applied his expertise to the development of the network features and the framework for vertical applications. The development of the ArcMap™ and ArcCatalog™ applications was led by Barry Michaels, Scott Simon, and Keith Ludwig. The accessibility and consistency of the software user interface was guided by Rupert Essinger. This complex endeavor was orchestrated by Matt McGrath. Many product specialists and programmers at ESRI provided material for this book and reviewed chapters. These include Andy MacDonald, Charlie Frye, Mike Minami, Aleta Vienneau, Jim TenBrink, Wolfgang Bitterlich, Tom Brown, Dale Honeycutt, Steve Kopp, Brett Borup, Peter Petri, Clayton Crawford, and Andrew Perencsik. The contributions of Andy, Dale, and Steve to chapters 5, 8, and 9 respectively are particularly noteworthy. The attractive city maps throughout this book were kindly provided by Gar Clarke, GIS manager at the City of Santa Fe, New Mexico. The image of Mars at the front of chapter 9 is courtesy of Malin Space Science Systems and JPL/NASA. The maps on the chapter title pages are drawn from the work of many cartographers from history. Their maps remind us that, although we have reached a level of sophistication in drawing maps with computers, we have yet to equal their artistry. Several people were actively engaged in the production of this book. Jennifer Wrightsell rigorously edited the chapters and designed the layout, along with Andy Mitchell and Youngiee Auh. Amaree Israngkura designed the cover. Michael Hyatt did the copyedit. Robin Floyd and Christian Harder managed and guided the publication of this book. Scott Morehouse wrote the preface and is ESRI’s visionary on advancing the theory and practice of GIS. Clint Brown prodded and inspired us to create the best product we had within ourselves. Curt Wilkinson and David Maguire worked hard to ensure that ArcInfo 8 meets the goals and requirements of users. Jack Dangermond created this very special and unique institute where we can believe that we make a difference in this world and act on that idea. Finally, my wife Elizabeth deserves special thanks for her countless hours of support. Her commitment and encouragement made the effort to produce this book possible. ... - tailieumienphi.vn