Possible to have 2 templates share logic?

I have a meteor app that I’m working on that display a map of business locations. The map has a an observe helper added in order to update itself reactively when business locations are added, deleted or changed in the collection.

  added: function(document) { ...

I also have a list of those locations (sites) in a table displayed underneath the map area and a list of “filters” (checkboxes) that allows the user to filter which businesses to view in the list / map. The filters set session variables that the list uses to update itself:

  sites: function() {
    // return Sites.find ({
    // return Sites.find({ "project": {$in: ["Home Depot POS", "Beer Shop POS Install"]}}, {
    var projectList = Session.get("projectList")
    if (projectList == null) {
      projectList = [];

  if (sitesToShow == "problemSitesOnly") {
      return Sites.find({ "project": {$in: projectList}, "client": {$in: clientList}, "siteStatus": {$in: ["2"]} }, {
        sort: {
          siteStatus: -1

My question is how can I get the map area to look at the session variables to update itself instead of using the .observe callback?