{"rowid": 163, "title": "Get To Grips with Slippy Maps", "contents": "Online mapping has definitely hit mainstream. Google Maps made \u2018slippy maps\u2019 popular and made it easy for any developer to quickly add a dynamic map to his or her website. You can now find maps for store locations, friends nearby, upcoming events, and embedded in blogs. \n\nIn this tutorial we\u2019ll show you how to easily add a map to your site using the Mapstraction mapping library. There are many map providers available to choose from, each with slightly different functionality, design, and terms of service. Mapstraction makes deciding which provider to use easy by allowing you to write your mapping code once, and then easily switch providers.\n\nAssemble the pieces\n\nUtilizing any of the mapping library typically consists of similar overall steps:\n\n\n\tCreate an HTML div to hold the map\n\tInclude the Javascript libraries\n\tCreate the Javascript Map element\n\tSet the initial map center and zoom level\n\tAdd markers, lines, overlays and more\n\n\nCreate the Map Div\n\nThe HTML div is where the map will actually show up on your page. It needs to have a unique id, because we\u2019ll refer to that later to actually put the map here. This also lets you have multiple maps on a page, by creating individual divs and Javascript map elements. The size of the div also sets the height and width of the map. You set the size using CSS, either inline with the element, or via a CSS reference to the element id or class. For this example, we\u2019ll use inline styling.\n\n<div id=\"map\" style=\"width: 400px; height: 400px;\"></div>\n\nInclude Javascript libraries\n\nA mapping library is like any Javascript library. You need to include the library in your page before you use the methods of that library. For our tutorial, we\u2019ll need to include at least two libraries: Mapstraction, and the mapping API(s) we want to display. Our first example we\u2019ll use the ubiquitous Google Maps library. However, you can just as easily include Yahoo, MapQuest, or any of the other supported libraries.\n\nAnother important aspect of the mapping libraries is that many of them require an API key. You will need to agree to the terms of service, and get an API key these.\n\n<script src=\"http://maps.google.com/maps?file=api&v=2&key=YOUR_KEY\" type=\"text/javascript\"></script>\n<script type=\"text/javascript\" src=\"http://mapstraction.com/src/mapstraction.js\"></script>\n\nCreate the Map\n\nGreat, we\u2019ve now put in all the pieces we need to start actually creating our map. This is as simple as creating a new Mapstraction object with the id of the HTML div we created earlier, and the name of the mapping provider we want to use for this map. \n\nWith several of the mapping libraries you will need to set the map center and zoom level before the map will appear. The map centering actually triggers the initialization of the map. \n\nvar mapstraction = new Mapstraction('map','google');\nvar myPoint = new LatLonPoint(37.404,-122.008);\nmapstraction.setCenterAndZoom(myPoint, 10);\n\nA note about zoom levels. The setCenterAndZoom function takes two parameters, the center as a LatLonPoint, and a zoom level that has been defined by mapping libraries. The current usage is for zoom level 1 to be \u201czoomed out\u201d, or view the entire earth \u2013 and increasing the zoom level as you zoom in. Typically 17 is the maximum zoom, which is about the size of a house. \n\nDifferent mapping providers have different quality of zoomed in maps over different parts of the world. This is a perfect reason why using a library like Mapstraction is very useful, because you can quickly change mapping providers to accommodate users in areas that have bad coverage with some maps. \n\nTo switch providers, you just need to include the Javascript library, and then change the second parameter in the Mapstraction creation. Or, you can call the switch method to dynamically switch the provider.\n\nSo for Yahoo Maps  (demo):\n\nvar mapstraction = new Mapstraction('map','yahoo');\n\nor Microsoft Maps (demo):\n\nvar mapstraction = new Mapstraction('map','microsoft');\n\nwant a 3D globe in your browser? try FreeEarth (demo):\n\nvar mapstraction = new Mapstraction('map','freeearth');\n\nor even OpenStreetMap (free your data!)  (demo):\n\nvar mapstraction = new Mapstraction('map','openstreetmap');\n\nVisit the Mapstraction multiple map demo page for an example of how easy it is to have many maps on your page, each with a different provider. \n\nAdding Markers\n\nWhile adding your first map is fun, and you can probably spend hours just sliding around, the point of adding a map to your site is usually to show the location of something. So now you want to add some markers. There are a couple of ways to add to your map.\n\nThe simplest is directly creating markers. You could either hard code this into a rather static page, or dynamically generate these using whatever tools your site is built on.\n\nvar marker = new Marker( new LatLonPoint(37.404,-122.008) );\nmarker.setInfoBubble(\"It's easy to add maps to your site\");\nmapstraction.addMarker( marker );\n\nThere is a lot more you can do with markers, including changing the icon, adding timestamps, automatically opening the bubble, or making them draggable. \n\nWhile it is straight-forward to create markers one by one, there is a much easier way to create a large set of markers. And chances are, you can make it very easy by extending some data you already are sharing: RSS. \n\nSpecifically, using GeoRSS you can easily add a large set of markers directly to a map. GeoRSS is a community built standard (like Microformats) that added geographic markup to RSS and Atom entries. It\u2019s as simple as adding <georss:point>42 -83</georss:point> to your feeds to share items via GeoRSS. Once you\u2019ve done that, you can add that feed as an \u2018overlay\u2019 to your map using the function:\n\nmapstraction.addOverlay(\"http://api.flickr.com/services/feeds/groups_pool.gne?id=322338@N20&format=rss_200&georss=1\");\n\nMapstraction also supports KML for many of the mapping providers. So it\u2019s easy to add various data sources together with your own data. Check out Mapufacture for a growing index of available GeoRSS feeds and KML documents. \n\nPlay with your new toys\n\nMapstraction offers a lot more functionality you can utilize for demonstrating a lot of geographic data on your website. It also includes geocoding and routing abstraction layers for making sure your users know where to go. You can see more on the Mapstraction website: http://mapstraction.com.", "year": "2007", "author": "Andrew Turner", "author_slug": "andrewturner", "published": "2007-12-02T00:00:00+00:00", "url": "https://24ways.org/2007/get-to-grips-with-slippy-maps/", "topic": "code"}