Compilation of GIS data for the Lower Brazos River basin

Transcription

1 Compilation of GIS data for the Lower Brazos River basin Prepared by Francisco Olivera, Ph.D., P.E., Srikanth Koka, and Lauren Walker Department of Civil Engineering October 2, 2006 Contents: Brief Overview Goals of the Exercise Computer and Data Requirements Procedure: 1. Preparing HUCs Data 2. Preparing NHD Data 3. Preparing Roads Data Brief Overview The collection of data is one of the most important steps when building projects in GIS. This exercise can be taken as a template for data collection. In this exercise you will download data for the Lower Brazos River Basin. The data you will be downloading consist of HUCs (Hydrologic Unit Codes), NHD (National Hydrographic Dataset) streams, and roads. HUCs will be obtained from the TWDB (Texas Water Development Board); NHD from the USGS (United States Geologic Survey); and roads from the TNRIS (Texas Natural Resources Information System). The data will be obtained in compressed format. This exercise will introduce you to the process of uncompressing the data that are in e00 format using ArcView 9.0 tools. Goals of the Exercise This exercise is intended to introduce you to the practice of obtaining data from different sources. Department of Civil Engineering

2 Computer and Data Requirements This exercise has been successfully completed using ArcGIS 9.0. Before starting, a description of the data is given. Data Description HUC: The USGS has classified the United States into hydrologic units. There are 4 levels of classification. These classifications are based on the amount of geographic area covered in each unit. The first level of classification divides the nation into 21 regions. The second level classification divides these 21 regions into 222 sub-regions, which are further divided into 352 hydrologic accounting units by the third level of classification. The fourth level of classification further divides the hydrologic accounting units into 2150 cataloging units. The Lower Brazos Basin lies in Region 12. For information on HUCs visit NHD: NHD is a comprehensive digital spatial dataset that contains information about surface water features in the United States. For information on NHD, visit The image below shows the Lower Brazos Basin highlighted in red. Department of Civil Engineering 2

3 Procedure 1. Preparing HUCs Data A. Download HUCs data for Texas (1) Make a working folder in one of the drives in your computer to store all the data that will be downloaded during this exercise. (2) Download the HUCs data from the TWDB. Click on the following link to visit the TWDB page containing GIS data: (3) Scroll down the page until you see Hydrologic Unit Code (HUC) data link, which exists under the Natural Features data section. (4) On the right side of the link you should see three download icons. The first can be used if the data is to be downloaded in geodatabase format, the second one is for downloading in shapefile format and the third one is for downloading the metadata for the data. For this exercise you will first download the HUCs data of Texas in shapefile format. You will later extract data for the Lower Brazos Basin from this. To download the HUCs data in shapefile format, click on the polygon shapefile icon beside the HUC link. Department of Civil Engineering 3

4 (5) A file download form opens. In this form, click the Save button. (6) In the window that opens next, browse to the working folder, and using the default name tx_hucdd.zip save the zip file. When the download completes, click Close. (7) The downloaded data is in compressed format. You will need uncompress the data to the same folder by right-clicking on the zip file and then clicking on Extract All. A new folder called tx_hucdd will be created as you go through the wizard. The HUCs shapefile named tx_hucdd.shp is found in this folder. This shapefile includes the data for the whole of Texas but we need data only for Lower Brazos. B. Extract HUCs data for Lower Brazos Basin from Texas HUCs (1) The next step is to extract the data for Lower Brazos from the tx_hucdd.shp. (2) Open a new ArcMap document and save the document as Texas.mxd in the working folder. (3) Once you have saved the document, add tx_hucdd.shp to a data frame in the ArcMap document. To add the shapefile, click on the AddData button, browse to the folder where the shapefile exists using the AddData wizard that opens. In the wizard, click on tx_huccdd.shp and then click on Add. The map document should look like the image below: (4) Once the Texas HUCs file is added to the map, right-click on the layer and Open Attribute Table by clicking on it. Among all the fields in the table you should see two fields called REG and SUBR. These fields refer to the region Department of Civil Engineering 4

5 number and the sub-region number of the cataloging units, and are key fields for extracting the data needed. Note that the Lower Brazos basin corresponds to Sub-region 7 in Region 12. The extraction of cataloging units for this area can be done using the Select by Attributes feature. (5) With the table open, click Options/ Select by Attributes. Then in the script window type REG = 12 AND SUBR = 7 (you can also single- or doubleclick on the Fields column, the mathematical operation buttons, and the Unique values column) and then click Apply to select features corresponding to the Lower Brazos basin in the map. (6) Click Close to close the Select by Attributes window. Close the attribute table after looking at the selected features. (7) As Lower Brazos HUC polygons are selected, export them to the working folder as a new shapefile. To do this, right-click on the layer and then click on Department of Civil Engineering 5

6 Data/Export Data. In the wizard that opens, with the option of Selected features chosen, use the default option. Use the same coordinate system as this layer's source data and click on the Folder icon. In the next wizard that appears, choose the working folder, type the name for the new shapefile as Low_Brazos_HUCs, click the Save button and then the OK button. (8) When prompted for adding the shapefile to the data frame, click Yes to add the data to the data frame. Now unselect the features previously selected using Selection/Clear Selected Features. Your map should look similar to the image shown below. (9) This completes the compilation of HUCs data for Lower Brazos Basin. The next step is to obtain NHD streams for this area. Unselect the tx_hucdd layer so that you can see only the Low_Brazos_HUCs features. If you want to, zoom into this layer by right-clicking on it and then clicking Zoom to Layer. Department of Civil Engineering 6

7 2. Preparing NHD Data Before going into details about downloading NHD data, spend some time looking at the attribute table of the layer just added to the view (i.e., Low_Brazos_HUCs). Look at the values in the field named HUC in the table. There is a pattern among these values. For example, look at the HUC value of The 12 corresponds to the region, 07 corresponds to the sub-region, 02 corresponds to the accounting unit, and 01 corresponds to the cataloging unit. As in the case of extracting the HUCs, the region and sub-region attributes are also important to extract the NHD streams data. With this introduction you will now start downloading the NHD data. A. Download separate datasets for each cataloging unit (1) Go to the link ftp://nhdftp.usgs.gov/subregions/. Select the folder titled Medium. Select the folder titled NHDM1207.zip. (2) The cataloging units that start with 1207 are for the Lower Brazos corresponding to region 12 and sub-region 07. (3) You can download the data by clicking on the links given in this document or on the web page. Start downloading the data by clicking on the link and saving the zip file to your working folder. Department of Civil Engineering 7

8 (4) Now, using Window Explorer, go to the working folder to find the zip file named NHDM1207.zip. To uncompress this file, right-click on it and click Extract All. (5) An Extraction Wizard will appear to extract it to the working folder using the default options. Use the default options in the wizard. (6) As coverages cannot be viewed by using Windows Explorer, view them using ArcCatalog. Using ArcCatalog, browse down to the arc feature class of each cataloging unit as shown below. The following image shows an example of NHD data for 1207 for NHDFlowline. (7) Add all feature classes to the ArcMap document as described in step 3 of Part B of Section 1 and then unselect the Low_Brazos_HUCs layer to view the NHD streams properly. (When adding the feature classes, find the geodatabase click on it then click on Hydrography and select all of the feature class to add. Make sure the NHDFlowline is the one that is selected after all the feature classes are added.) Department of Civil Engineering 8

9 3. Preparing Roads Data In this step you are going to download roads data from the TNRIS website. The data you are going to download consists of road features for Texas that will later be clipped to extract data needed for the Lower Brazos region only. (1) To download the data go to ftp://ftp.tnris.org/. (2) You will see that in this page, the data are categorized under different folders such as Administrative, Biological, etc. Open the transportation folder for the roads data by double-clicking on the folder that says Transportation. Department of Civil Engineering 9

10 (3) In the next window there will be four sub-folders: Airports, Railroads, Roads and Waterways. The roads data exist inside the Roads folder. Double-click on the folder named Roads. (4) Inside the Roads folder you will see four sub-folders; click on the TSMS folder. TSMS refers to Texas State Mapping System projection. The data inside the TSMS folder is projected in Texas State Mapping System. (5) Inside the TSMS folder is the compressed file of roads data called highway_ts.zip. Now save this zip file to your working directory by clicking on Department of Civil Engineering 10

11 (6) the highway_ts.zip folder and clicking save then scrolling to your working folder and clicking save again. (7) Uncompress this file by right-clicking on the zip file and then by clicking Extract All. An Extraction Wizard will appear so make sure you use the default option and save the new folder to your working directory. Look at the contents inside the newly created folder and note the two files inside the folder. You will need the file named highway_ts.e00. The format e00 is used for distributing compressing coverages or DEMs. It is called an interchange file. A. Convert e00 file into a coverage The next step in the exercise is to uncompress this e00 file. Using the capabilities of ArcGIS, you can now extract the coverage. (1) Go to Start / Programs / Courseware / ESRI / ArcGIS 3.x / Import71. (2) Click on Browse next to ExportFilename and scroll to the file highways_ts.e00. Select this file and then click Open. (3) Click on Browse next to Import Data Source and find your working folder and add the new file with the name Roads. Department of Civil Engineering 11

12 (4) Click OK and the file will be exported. (5) Add the coverage to the data frame using Add data tool in ArcMap. This coverage includes the roads data for Texas, but only the roads data for the Lower Brazos River Basin is needed. B. Clipping the Texas roads data to obtain data for the Lower Brazos River Basin (1) Make sure the hwy arc is highlighted (shown in the above screen shot) and then click on View/Data Frame Properties. Department of Civil Engineering 12

13 (2) Select the Data Frame tab and click on Enable/Specific Shape. (3) In the Data Frame Clicking wizard, select the Lower_Brazos_HUCs as the outline feature and you can make the decision on whether you would like to clip All Data Frames or just the Visible Data Frames. (4) Click on the OK then Apply and then OK. This will clip the data frame to the Lower_Brazos_HUCs. Now that you have compiled data for Lower Brazos Basin, take a little time and look at the spatial reference properties of the datasets you have compiled as a part of this exercise because it is always good practice to make sure that datasets have defined projections. To view spatial reference properties of a layer, right click on the layer/properties/ Source. Observe that Roads, Low_Brazos_NHD, Low_Brazos_HUCs and tx_hucdd are all in GCS_North_American_1983 projection, where as roads arc is in Lambert Conformal Conic projection. This shows that data downloaded from different sources may have different projections. To have consistency in projection among all the datasets compiled for projects in GIS, use ArcToolBox to create new datasets that will all be in same projection. Another thing that should be noted is that even though the roads arc dataset was in a different projection compared to others, all the layers still overlay on one another because Department of Civil Engineering 13

14 of ArcMap s capability called Projection on fly. Though this is convenient, the projection is temporary. To have a permanent projection for datasets, create a new projected dataset using the available tools. These materials may be used for research and educational purposes only. Please credit the authors and the Department of Civil Engineering,. All commercial rights reserved. Copyright 2004:. Department of Civil Engineering 14