Module 10 Data-action models

Transcription

1 Introduction Geo-Information Science Practical Manual Module 10 Data-action models

2 10. INTRODUCTION 10-1 DESIGNING A DATA-ACTION MODEL 10-2 REPETITION EXERCISES 10-6

3 10. Introduction Until now you have applied various GIS processing tools to solve basic spatial problems and questions. However, during your professional career you will be confronted with more complex geographical analyses that require many input datasets and (interconnected) geoprocessing steps before a certain spatial problem is solved. When you want to tackle a complex spatial problem you should first study the problem. This involves asking the following questions: What output dataset(s) are exactly demanded? What input datasets are available? What geoprocessing steps can be distinguished within the analysis process and are there connections between steps? What are the inputs and outputs of the geoprocessing steps? What data handling classes can be utilized for these (interconnected) geoprocessing steps? These questions must be answered and the answers must subsequently be formalized in a data-action model before you start using any GIS software. The data-action model shows the whole analysis process from input datasets to output datasets, all required geoprocessing steps and intermediate results. The dataaction model helps you keep track of what you are doing when implementing the analysis process in a GIS software package. In this module: The data-action model. Repetition exercises. Objectives After having completed this module this part you will be capable: to analyze a spatial problem and to identify required input datasets, the geoprocessing steps and desired output datasets. to design a data-action module for a spatial problem. ArcMap document: Literature: Data-action models.mxd This module 10-1

4 Designing a data-action model When you want to tackle a spatial problem using GIS software, you start with a conceptual data model of reality. This model describes the characteristics and functional relationships between real-world phenomena in context of your spatial problem. The next step is translating the conceptual data model to a logical formal data model that guides you in your GIS implementation. The logical formal data model defines which input datasets are used in an application and in which order. It also specifies all successive geoprocessing steps that have to be carried out on the input datasets. Finally the logical formal data model lists the output datasets; these include not only the end result(s) but also the intermediate results (output datasets from various geoprocessing steps that are used as input for the next processing step). A formal presentation of a logical data model can be in form of a data-action model. A data-action model gives a structured overview of the methodological framework to solve a spatial problem, in form of a flow chart (Figure 1). There are certain rules you have to abide by when designing a data-action model. Datasets are presented by parallelograms, ovals and rectangles. This separation is made to be able to distinguish the different data structures. Parallelograms represent raster structured data whilst ovals represent vector structured data. Certain geoprocessing steps only include a thematic attribute table. These are represented as rectangular blocks. The geoprocessing steps that are carried out on the datasets are represented by the arrows. Each arrow is accompanied by a symbol that represents the data-handling class. There are three different symbols, one for each data-handling class: lightning bolts represent transformations, question marks represent queries and circles represent operations. Each arrow is followed by a new output dataset or, in case of a query, a set selected features or raster cells. Figure 1. The data-action model. Datasets and geoprocessing steps are numbered. Every input dataset has the number 0 followed by an alphabetically ordered letter. Every geoprocessing step has a number. The first step gets number 1. Every dataset that becomes a result of a geoprocessing step gets the number of the step followed by an alphabetically ordered letter. When the data-action model is examined thoroughly at the logical formal level, it can be transferred to a GIS environment, e.g. ArcMap. This is referred to as the implementation level. The various processing steps are carried out by means of the available commands (procedures). The GIS user often finds that not all processing steps discerned in theory, are available in the GIS package used. Or that two processing steps are executed with only one procedure. It may also occur that certain processing steps are not 10-2

5 included by means of one command (or one procedure), but has to be realized by means of several commands (procedures). Figure 2 gives an example of a data-action model to solve a problem that could be: What are suitable lotions for a the construction of a new residential area, taking into account noise pollution by airplanes, the soil type and the regional land use plan. Figure 2. A data-action model for a location problem. soil type region plan airport selection vector-raster transformation buffering sandy soils region plan noise pollution zone selection selection building locations No noise pollution overlay potential building locations The course Geo-information Tools (GRS 20806) treats the use of data-action models, including notation, and GIS application building in more detail. 1. In Figure 3 you see an example of a data-action model. a. Have a look at the Figure 3 and try to find out if there is something wrong with the notation of this model and if so, write down what is wrong, why it is wrong and how to improve it. 10-3

6 Figure 3. Example of a data-action model that contains some errors. 10-4

7 2. The municipality boards of Wageningen, Rhenen, Veenendaal and Ede decided to start an investigation for the building of a new multi-functional soccer stadium. You as a beginning GIS expert were asked to advise the municipality boards where to locate this new stadium. AVAILABLE DATA a dataset of all municipalities and places in the Netherlands (vector structure); a dataset with information about land use in the four municipalities (vector structure); a dataset with information about soils in the Netherlands (raster structure); a dataset with information about all the roads in the Netherlands (vector structure); a dataset with information about elevation (raster structure). CONDITIONS The new stadium has to be located: within a circle of 2000 meters of the center of a city with a railway station; within a distance of 1000 meters of an existing highway; on soil with a sandy underground; 7.5 meters above sea-level; not in a nature reserve. a. Draw a complete data-action model for finding suitable locations for this new multi-functional stadium. Make use of all datasets and think of the conditions. Of course there is more then one solution. Discuss your results with your neighbor(s). 10-5

8 Repetition exercises This section contains exercises with more challenging GIS assignments than you have had so far. These exercises are to test whether you have understood the content of the ArcGIS modules. And besides that, the exercises give the opportunity to practice data-action model design. Try to do these exercises without help of the practical supervisors. If you are finished, discuss your answers with the practical supervisors. 3. Open ArcMap document Data-action models.mxd. Activate data frame Exercise 3. a. Open the attribute table of dataset Land_use. Fill in Table 1. The feature type The number of features The number of records The number of fields The number of attributes Table 1. Analyzing the attribute table of a dataset. Answer the following question: What are the ph-values of the soil profile points, which are located within the land use features adjacent to forest features (C2=3)? b. Write down this query according to the formal structure format of a SQL query. Select: From: Where: c. Write down this query step by step in Table 2. Dataset Description ArcMap's functionality Query type Result Table 2. The query step by step. Write down for every step the dataset that is queried, a short description of the step, the ArcMap tool used for the step, query type (tabular or spatial) and a drawing of the result. d. What are the ph values? 10-6

9 4. Activate data frame Exercise 4. The Centre for Geo-information has been very successful the last five years in education and research and is growing so fast that the staff decided to move to a new building somewhere in the south of Wageningen. You, as GIS experts have been asked to map where the suitable areas in the southern part of Wageningen for building this new Centre for Geo-information are located. The suitable locations for the new buildings are based on the following conditions: To save costs, the new building has to be built on a sandy soil; soils classified as Holtpodzolgrond seem suitable. The new building has to be located within 100 meters from the nearest road. Only locations with a slope angle between 10 and 25 are suitable. Slopes facing South or South-East are suitable. The total area for the new building, parking place, etc. has to be at least 1300 m 2. Set Analysis Extent and Analysis Mask to LU_raster. NEW TOOL: at a certain point in the analysis you have to use a tool that has not been discussed in one of the previous modules: Region group. Consult ArcGIS Desktop Help system to learn more about this tool. Find out yourself at what point during the analysis you will have to use the tool. a. Create a data-action model for this assignment and implement the designed process in ArcMap. b. How many m 2 are potentially suitable for the building of a new Centre for Geo-Information? Explain your answer? The last part of this exercise is a bit more challenging. Hint: work with tables (dbf) when you want to do calculations with raster attributes. You can calculate areas with the Zonal Geometry tool, which can also give TABULAR output. Use the tools ADD / DELETE field, Join and export (right-click table, point to Data, click Export) to solve the next question. Try not to use your pocket calculator when you calculate areas or ratios; solve it using ArcMap. See also module 2 for attribute calculations (Data management toolbox). Make sure tables are NOT opened when you add or delete fields. A you did the calculations, the table with the results can be joined to the raster dataset with the suitable locations. c. What part of the potential locations (%) is covered by forests? Write down the data-action model and explain your answer. 10-7

10 5. Activate data frame Exercise 5. Answer the following question: What is the total area of each land use type within 250 meters of the Gen. Foulkesweg? Use raster dataset LU_raster. Set Analysis Extent and Analysis Mask to LU_raster. a. Create a data-action model for this assignment and implement the designed process in ArcMap. What is the total area? 10-8