TerraMap Web is a cross-platform, interactive Terraria v1.4.4 world map viewer that loads quickly and lets you pan, zoom, find blocks, ores, items in chests, dungeons, NPCs, etc.
TerraMap uses only a single pixel and color for each block, tile, wall, item, etc. It does not use the game's textures. For that, I highly recommend the excellent Terrafirma.
It's built using JavaScript, JQuery, and Bootstrap. It uses Web Workers to do processor-intensive work in the background to improve responsiveness and performance.
I experimented with several different approaches to drawing, and finally ended up using HTML canvas 2d context fillRect method, which is the fastest method on Chrome, my current browser of choice.
This was an education exercise for me. The only real improvements I made over Terrafirma are the combined block/tile/item search, allowing you to search for items in chests, the incremental search forward/backward, and UI improvements.
I referenced the Terraria .wld format documentation provided by Terrafirma to read the world data. Sean definitely did a great job at reverse-engineering and documenting the format. Portions of TerraMap code were adapted from the source code for TerraFirma and TEdit. I also used ILSpy to peek at some of the Terraria game code.
I used the excellent jquery.panzoom for pan and zoom functionality.