Mapping wind speed and direction in Antarctica An example of the work of the BAS Mapping and Geographic Information Centre The data: Step 1: Format the data • Spreadsheet with latitude, longitude, wind-speed and direction. • Ensure the format is GIS compatible (no spaces in the column title and only numeric values in the columns). • Save as a .csv file. • Make sure that you close the spread-sheet after you have saved it. • In this spreadsheet we have the required geographic information (latitude and longitude) and two attributes; wind magnitude (magnitude) and wind direction (dir). Step 2: Create the point file (a) • Open ArcCatalogue. • Click on create feature class, and then from Xytable. • This should bring up a dialogue box as shown on the next slide. Step 2: Create the point file (b) • Make sure that the X field is Longitude and the Y is Latitude. Click the Coordinate System button. • Navigate to select Geographic Coordinate Systems/World/WGS84.prj. • Save this file in an appropriate directory as XYwinds and press OK. • This operation will transform the spreadsheet into points. Step 3: Bring into Arcmap • • • • Open ArcMap. Let's add some data to the map. First we will add a coastline as a reference. Use the Add data button, navigate to your folder and add the coastline file. • Now using the same button add the newly created point data-set. • When that has come in click on the XYwinds file in the table of contents on the left hand side and drag it so that it is below the coastline . • The result should look like the next slide. detail Step 4: Visualize the coastline • The next step is to visualize the various datasets. Let’s do the coastline first. • In the table of contents on the left hand side left click on the coastline layer. • At the bottom click on Properties, then click on the Symbology tab at the top of the resulting box. • This will bring up a dialogue box similar to the one below. • By clicking on the Symbol button you can change the coastline colour and thickness to a style you prefer. Step 5: Visualize the wind data - by size (a) • Now lets do the same with the wind data. • We will change the symbol to an arrow and turn the arrow to the direction based on the pol_direction attribute in the dataset. • At the same time we can change the size of the arrow to reflect the magnitude of the wind. Step 5: Visualize the wind data - by size (b) • Right click on the layer and go into the Properties and open the Symbology tab. • In the panel on the left hand side of the box change from the default of Features, to the Quantities option. • Choose the middle option of Graduated Symbols. • Then in the box that reads Value change the field to Magnitude - this changes the symbol size to reflect the magnitude of the wind. • Click OK and if necessary use the zoom and pan tools to investigate the data. Step 6: Visualize the wind data - by direction (a) • Go back into your symbology. • On the right hand side there is a button called Template. • Click on this, it will bring up the Symbol selector. Step 6: Visualize the wind data - by direction (b) • Click on More Symbols and tick the Business symbol set. • Using the scroll bar scroll down until you reach the arrows and choose Arrow Up (circled in red left). • Now click on the Advanced button at the bottom of the main panel and choose Rotation. • Change the field selector to dir and ensure the radio button is on Arithmetic. Click ok, this links the direction to the attribute in the data-set. • Change the symbol size boxes so that the symbols range between 3 to 10 points. • Check that your symbology window looks similar to the one below and click ok. Step 7: Investigate the data • Your data should now look like the next slide. • Have a look at the detail of the data to see how the size and direction of the arrows face. Step 8: Add a digital elevation model (DEM) • Use the Add Data button to add the digital elevation model called Dem. • Go into the data frame properties as before (View > dataframe properties), but this time into the Dem file. • Experiment with colour ramp in the symbology until you are happy with the colours. • Have a look at the result. Does the wind direction follow the topography in any way? Step 9: Investigation in detail • Look in detail at the data. Can you see any relationship between the wind and the topography? • The answer is that winds in Antarctica, especially winter winds are Katabatic; they flow downhill and are fastest where the slopes are steepest. • On the coast they are affected by local cyclonic winds which then divert them anticlockwise.