Compilation of GIS data for the Lower Brazos River basin

Transcription

1 Compilation of GIS data for the Lower Brazos River basin Francisco Olivera, Ph.D., P.E. Srikanth Koka Lauren Walker Aishwarya Vijaykumar Department of Civil Engineering December 5, 2011 Contents Brief Overview... 1 Goals of the Exercise... 2 Computer and Data Requirements... 2 Procedure Preparing HUCs Data... 3 A. Download HUCs data for Texas... 3 B. Extract HUCs data for Lower Brazos Basin from Texas HUCs Preparing NHD Data... 8 Download separate datasets for each cataloging unit Preparing Roads Data A. Clipping the Texas roads data to obtain data for the Lower Brazos River Basin Convert e00 file into a coverage Brief Overview The collection of data is one of the most important steps when building projects in GIS. This exercise will help you practice data collection for GIS projects. 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 you obtain will be in the compressed format. This exercise will introduce you to the process of uncompressing the data that are in e00 format using ArcView 10. Department of Civil Engineering

2 Goals of the Exercise This exercise will introduce you to obtaining data from different sources. Computer and Data Requirements This exercise has been completed using ArcGIS 10. A description of the data is given below. 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, under the Natural Features data section. Department of Civil Engineering 3

4 (4) TWDB gives you the option of downloading the HUCs data as a geodatabase or as a shapefile. For this exercise, you must download the HUCs data of Texas in shapefile format. You will then extract the data for the Lower Brazos Basin from this. To download the HUCs data in shapefile format, click on the HUC Shapefile link. Save the tx_hucdd.zip file to your working folder. (5) 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 to tx_hucdd\. A new folder called tx_hucdd will be created. The HUCs shapefile named tx_hucdd.shp should be in this folder. This shapefile contains 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 The next step is to extract the data for Lower Brazos from the tx_hucdd.shp file. Department of Civil Engineering 4

5 (1) Open a new ArcMap document and save the document as Texas.mxd in the working folder. (2) 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: (3) Once the Texas HUCs file is added to the map, right-click on the layer and click Open Attribute Table. Among all the fields in the table, you should see two fields called REG and SUBR. These fields refer to the region 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. Use the Select by Attributes tool to extract the area using the cataloging units. (4) With the table open, click Options/Select by Attributes. Then in the script window, type REG = 12 AND SUBR = 7 (use the entries in the Fields column, the mathematical operation buttons, and the Unique values column to avoid errors) and then click Apply to select features corresponding to the Lower Brazos basin in the map. Department of Civil Engineering 5

6 (5) Click Close to close the Select by Attributes window. (6) Keeping the Lower Brazos HUC polygons selected, right click on the layer and then click on Data/Export Data. In the Export Data window, choose the Selected features option Department of Civil Engineering 6

7 chosen and use the same coordinate system as this layer s source data. Browse to the working folder and type the name for the new shapefile as Low_Brazos_HUCs; click the Save button and then the OK button. (7) 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. (8) This completes the compilation of HUCs data for Lower Brazos Basin. The next step is to obtain the 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 7

8 2. Preparing NHD Data Before going into the details of downloading NHD data, spend some time looking at the attribute table of the Low_Brazos_HUCs layer in ArcMap. Look at the values in the field named HUC in the table. There is a pattern to these values. For example, look at the HUC value 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. The region and sub-region attributes are important for extracting the NHD streams data. The following steps must be followed to extract the required NHD data. Download separate datasets for each cataloging unit (1) Go to the link ftp://nhdftp.usgs.gov/datasets/staged/subregions/personalgdb/. You can also access this folder from the website Select the folder titled MediumResolution. Find the folder titled NHDM1207_92v200.zip. (2) The cataloging units that start with 1207 are for the Lower Brazos (which is in region 12 and sub-region 07). Department of Civil Engineering 8

9 (3) Save the NHDM1207_92v200.zip file to your working folder. Uncompress this file, as described earlier. The NHDM folder should contain a coverage called NHDM1207. (4) Coverages cannot be viewed using Windows Explorer; open this file using ArcCatalog. Using ArcCatalog, browse down to NHDM1207 database and explore the contents of the feature classes. The following image shows an example of NHD data for 1207 for NHDFlowline. (5) Add all the feature classes under the Hydrography feature dataset inside the NHDM 1207 geodatabase to the ArcMap document Texas.mxd in ArcMap. Make NHDFlowline the only visible layer to view the NHD streams. (When adding the feature classes, find the geodatabase, click on it, then click on Hydrography and select all of the feature classes in it to add them. Make sure the NHDFlowline is the one that is selected after all the feature classes are added.) Department of Civil Engineering 9

10 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 be clipped later to extract data for the Lower Brazos region only. A. Download road data for Texas (1) To download the data go to (2) You will see that in this page, the data are categorized under different categories such as Bathymetry, Cultural, Indices, Transportation, etc. Department of Civil Engineering 10

11 (3) Under Transportation, there are links to four sub-categories: Railroads, Airports, StratMap Trans FGDB, and TxDOT Roadways. Click on the link labeled TxDOT Roadways. Save the TxDOT_Roadways.zip file to your working folder. (4) Uncompress this file. The newly created folder 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) Add the TxDOT_Roadways.shp file to Texas.mxd in ArcMap. Department of Civil Engineering 11

12 (2) Right click on in the Table of Contents and then click Properties. (3) Under Clip Options, select the Clip to shape in the dropdown menu and then click on Specify Shape... (4) In the Data Frame Clipping window, choose the Outline of Features as the option. Select the Lower_Brazos_HUCs layer as the outline feature. Now, make a decision about whether you would like to clip All data frames or just the Visible data frames. Department of Civil Engineering 12

13 (5) Click on the OK then Apply and then OK. This will clip the data frame to the Lower_Brazos_HUCs layer. Now that you have compiled data for the 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; it is always good practice to make sure that datasets have defined projections. To view the spatial reference properties of a layer, right click on the layer and then Properties/Source. Observe that TxDOT_Roadways.shp, NHDFlowline, Low_Brazos_HUCs, and tx_hucdd are all in the GCS_North_American_1983 projection. However, 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 the same projection. Another point that should be noted is that even though a dataset is in a different projection compared to others added to ArcMap, all the layers still overlay on one another because of ArcMap s capability called Projection on the fly. Although this is convenient, the projection assigned to a layer in this manner is temporary. To have a permanent projection for datasets, create a new projected dataset using the available tools. Department of Civil Engineering 13

14 4. Convert an e00 file into a coverage It may so happen that the data you require for a project is available only in the.e00 format. An.e00 file is an ArcInfo interchange file that can be converted into a coverage. Many sources online offer data in the.e00 format as these types of files are easier to transfer and share than other ArcGIS file formats. In this part of the tutorial, you will learn how to extract a coverage from an e00 file. (1) Open a new ArcMap document. (2) In ArcToolbox, browse to Conversion Tools/To Coverage/Import from E00. (3) Open the Import from E00 tool. (4) Click on browse button next to Input interchange file and add the E00 file that you downloaded. Select your working folder as the Output folder. Give a name to the coverage in the Output Name file. Click OK and the file will be exported. Department of Civil Engineering 14

15 (5) Add the coverage to the data frame using Add data tool in ArcMap. 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 2011:. Department of Civil Engineering 15