The contour line on a map represent lines, straight or curved, describing the intersection of a surface by interpolating one or more horizontal planes, forming gradients on the estimated variable or parameter, in order to interpret graphically. For example, a isohyet, isothermal and isobaric representing precipitation, temperature and pressure respectively in a time unit on a surface. In this post shows the procedure for isolines (isohyets, isotherms, isobars) in ArcGIS, based on meteorological stations distributed around the province of Loja. To create a isolínea is necessary to have a layer of weather stations to points (recommended minimum three), geo-referenced, and with a defined projection. If the weather information is within an Excel spreadsheet, you can add in ArcMap with the Add XY Data tool, then export the table as shapefile (Right click on the layer >, Data >, Export Data). In this section there is a set of tools for interpolation, according to the ArcGIS Resource Center conceptualized as follows: In Input point features select the point layer (weather stations). Z value field select field that contains the data of the isolines (precipitation, temperature, pressure, etc.). Output surface raster selecting the directory, you can also make additional adjustments to raster. In the dialog box fill data Input raster select the previously created raster (Kriging), Output polilyne features define the directory to save the shapefile and Contour Interval allows you to set an interval of isolines, this depends on the surface, variance and parameters under technical criteria. If you require vector polygons is necessary to reclassify the raster (Spatial Analyst Tools >, Reclass >, Reclassify) and then transform as vector (Conversion Tools >, From Raster >, Raster to Polygon). The interesting thing is that ArcGIS has a powerful toolset that allow us to reach a goal in various ways. Source.