# Geo-Referenced Graph
Geo-Referenced graphs are parametrized graphs which are translated into the coordinates of an image and drawn on top.
They are used for e.g. GIS-Data on top of a topological map or to draw the water level gauge measurements onto a (schematic) drawing of the dam.
# Geo-Referenced Image
First, you need to geo-reference an image that is to define for two points/pixels the exact coordinates they represent in real-life.
# Drawing on a Topological Map
Having the X- and Y- coordinates in two time series, you can select these two in your TisGraph MDA DataURL. The X is the "main" and the Y is the "secondary" one.
# Drawing of Water Level Gauges
You can use the const-vector feature to draw these onto a schematic drawing of your hydrodam.
The y-coordinate is given by the main time series. The x-coordinates are set to a const (only x1 is set) or to a linear function using the time series' y as its parameter using the basis vector (x1, y1) and direction vector (x2-x1, y2-y1).
You might probably want to use multiple time series combined feature as well to draw several gauges side-by-side with a line in between or a combined caption.