Issues #182: done.

src/components/Discover/Map/Filter/Trace.vue

@@ -215,8 +215,8 @@ export default {
             ticks: { // 設定間隔數值
               display: false, // 隱藏數值，只顯示格線
               min: 0,
-              max: this.traceList[0].ratio,
-              stepSize: (this.traceList[0].ratio)/4,
+              max: this.traceList[0]?.ratio,
+              stepSize: (this.traceList[0]?.ratio)/4,
             },
             grid: {
               color: 'rgba(100,116,139)',