# Map Scales CGView uses 3 different scales (x, y, bp) to keep track of map coordinates and basepair position. The scales are [d3.scaleLinear](https://github.com/d3/d3-scale#linear-scales) objects and map a continuous input domain to a continuous output range. The x and y scales relate the canvas (range) to the map coordindates (domain). The canvas origin is in the top left of the viewer and the coordinates move in a positive direction towards the bottom-right. The map origin in the center of the map (0,0) and the coordinates move in a positive direction towards the top-right. The bp scale differs depending on the layout: - Circular: the bp scale converts the circle angle to a basepair. This scale is not zoom dependent. - Linear: the bp scale converts basepair to distance on the x axis. This distance is zoom dependent. The scales are accessed directly through the viewer object, here shown as cgv. ```js cgv.scale // => {bp: function, x: function, y: function} ``` ## Circular Layout --- ## Linear Layout