GPS for Dummies.pdf - Engineering Surveyor

Chapter 15: Creating and Using Digital Maps with OziExplorer257Figure 15-5:A scannedandcalibratedOziExplorermap withwaypointsand tracks.Maps that are made for general information purposes (such as park visitormaps or maps in textbooks) are usually difficult to calibrate correctly becausethey don’t have the level of accuracy as navigation or survey maps do. (In fact,they’re more of diagrams — not maps — because they don’t have projections.)The actual locations of features shown on the map might not be correct, anddistances and proportions might not be accurate.Checking your workAfter you load and calibrate a scanned map, always check to make sure thatyour calibration was correct. Here are some ways to do this: Select Grid Line Setup from the Map menu. This allows you to overlaylatitude and longitude grid lines over the map. The overlaid grid linesshould match with the grid lines on the map or the coordinate marks onthe map edges.On USGS topographic maps, don’t get latitude and longitude lines confusedwith the more predominant Township and Range lines. (To findout the difference between latitude and longitude and Township andRange, read Chapter 2.)