Vector image:
Vector images are made up of many individual, scalable objects. These objects are defined by mathematical equations rather than pixels, so they always render at the highest quality. Objects may consist of lines, curves, and shapes with editable attributes such as color, fill, and outline. Changing the attributes of a vector object does not effect the object itself. You can freely change any number of object attributes without destroying the basic object. An object can be modified not only by changing its attributes, but also by shaping and transforming it using nodes and control handles.
向量圖是由許多單獨的、可拓展的元件所組成。這些元件是由數學方程式所定義，而非像素。因此它能夠保持在最好的狀況。
這些元件包括可以改變顏色、填充內容及外觀的直線、曲線或形狀。改變這些元件的屬性並不會使得元件本身受到任何影響。
你可以任意地修改這些元件的屬性而不會損毀元件基礎的內容。向量圖不只可以藉由修改其屬性來修改，也可以使用節點或者控制點來朔形跟變形。
(reference: http://graphicssoft.about.com/od/aboutgraphics/a/bitmapvector_2.htm)
Raster image:
In computer graphics, a raster graphics image, or bitmap, is a dot matrix data structure representing a generally rectangular gird of pixels, or points of color, viewable via a monitor, paper, other display medium. Raster images are stored in image files with varying formats.
在電腦圖像中，網格圖(亦稱點陣圖)是一種使用點矩陣資料結構來表現螢幕、紙張及其他顯示環境可見的方格像素或顏色點。網格圖可以儲存成許多不同圖檔格式。
(reference: http://en.wikipedia.org/wiki/Raster_graphics)
Bitmap images are resolution dependent. Resolution refers to the number of pixels in an image and is usually stated as dpi (dots per inch) or ppi (pixels per inch). Bitmap images are displayed on your computer screen at screen resolution: approximately 100 ppi. However, when printing bitmaps, your printer needs much more image data than a monitor. In order to render a bitmap image accurately, the typical desktop printer needs 150-300 ppi.
點陣圖是一種輸出結果取向的圖。輸出結果倚賴於圖形像素的數目，通常以dpi或者ppi來顯示。點陣圖在你的電腦的輸出結果大約是100 ppi；然而，當你在畫點陣圖時，你的繪畫工具所輸出的像素需要高於螢幕的輸出像素。因此，為了維持點陣圖的精確性，典型的電腦繪圖工具需要150-300 ppi。
(reference: http://graphicssoft.about.com/od/aboutgraphics/a/bitmapvector.htm)
上課心得:
這個禮拜的課程，提到了有關QGIS裏頭關於一般圖像掃描進去電腦之後，將圖像的影像座標定位在大地座標中，使得這張地圖有它的實用性及準確性；再將圖像載入QGIS並且定位之後才發現，原來影像在轉換座標的過程中會出現誤差，而且在有限的測量座標數據下，需要修正的部分一定會出現，若要把精確度提高，勢必需要相當多的測量數據。
